[payslip-ingest] Update extractor agent + dashboard for v2 regex parser

## Context

Companion change to payslip-ingest v2 (regex parser + accurate RSU tax
attribution). The Grafana dashboard now has 4 more panels powered by the
new earnings-decomposition and YTD-snapshot columns, and the Claude
fallback agent's prompt is aligned with the new schema so non-Meta
payslips still land with the full field set.

## This change

### `.claude/agents/payslip-extractor.md`

Rewrites the RSU handling section to match Meta UK's actual template
(rsu_vest = "RSU Tax Offset" + "RSU Excs Refund", no matching
rsu_offset deduction — PAYE uses grossed-up Taxable Pay instead).
Adds a new "Earnings decomposition (v2)" section telling the fallback
agent how to populate salary/bonus/pension_sacrifice/taxable_pay/ytd_*
and when to use pension_employee vs pension_sacrifice without
double-counting.

### `stacks/monitoring/modules/monitoring/dashboards/uk-payslip.json`

- **Panel 4 (Effective rate)** — SQL switched from the naive
  `(income_tax + NIC) / cash_gross` to the YTD-effective-rate
  method: `cash_tax = income_tax - rsu_vest × (ytd_tax_paid /
  ytd_taxable_pay)`. Title updated to "YTD-corrected" so the
  change is discoverable.
- **Panel 5 (Table)** — adds salary, bonus, pension_sacrifice,
  taxable_pay columns so row-level debugging against the parser
  output is trivial.
- **+Panel 8 (Earnings breakdown)** — monthly stacked bars of
  salary / bonus / rsu_vest / -pension_sacrifice. Bonus-sacrifice
  months show up as a massive negative pension_sacrifice spike
  paired with a near-zero bonus bar.
- **+Panel 9 (Accurate cash tax rate)** — timeseries of
  cash_tax_rate_ytd vs naive_tax_rate. Divergence is the RSU
  contribution the payslip hides in the single `Tax paid` line.
- **+Panel 10 (All-in compensation)** — stacked bars of cash_gross
  + rsu_vest per payslip.
- **+Panel 11 (YTD cumulative cash gross vs total comp)** — two
  lines partitioned by tax_year; the gap between them is the RSU
  contribution YTD.

Total panels go from 7 → 11.

## Test Plan

### Automated

Dashboard JSON validity:
```
$ python3 -m json.tool uk-payslip.json > /dev/null && echo ok
ok
```

### Manual Verification

After applying `stacks/monitoring/`:
1. `https://grafana.viktorbarzin.me/d/uk-payslip` loads with 11 panels
2. Bonus-sacrifice months (e.g. March 2024 if present in data) show the
   negative pension_sacrifice bar in panel 8
3. Panel 9 "Accurate cash effective tax rate" shows the
   cash_tax_rate_ytd line sitting ~10-15pp below naive_tax_rate in
   RSU-vest months

## Reproduce locally

1. `cd infra/stacks/monitoring && terragrunt plan`
2. Expected: ConfigMap diff on the payslip dashboard with the new panel
   JSON
3. `terragrunt apply` — Grafana reloads the dashboard automatically
   (configmap-reload sidecar)

Relates to: payslip-ingest commit 9741816

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

stacks/monitoring/modules/monitoring/dashboards/uk-payslip.json

@@ -288,7 +288,7 @@
     },
     {
       "id": 4,
-      "title": "Effective rate & take-home % (cash-basis)",
+      "title": "Effective rate & take-home % (cash-basis, YTD-corrected)",
       "type": "timeseries",
       "datasource": {
         "type": "grafana-postgresql-datasource",
@@ -361,7 +361,7 @@
             "type": "grafana-postgresql-datasource",
             "uid": "payslips-pg"
           },
-          "rawSql": "SELECT pay_date AS \"time\", ROUND(((income_tax + national_insurance)::numeric / NULLIF(gross_pay - rsu_vest, 0)) * 100, 2) AS \"effective_rate_pct\", ROUND((net_pay::numeric / NULLIF(gross_pay - rsu_vest, 0)) * 100, 2) AS \"take_home_pct\" FROM payslip_ingest.payslip WHERE $__timeFilter(pay_date) ORDER BY pay_date",
+          "rawSql": "SELECT pay_date AS \"time\", ROUND((((income_tax - (rsu_vest * COALESCE(ytd_tax_paid / NULLIF(ytd_taxable_pay, 0), 0))) + national_insurance)::numeric / NULLIF(gross_pay - rsu_vest, 0)) * 100, 2) AS \"effective_rate_pct\", ROUND((net_pay::numeric / NULLIF(gross_pay - rsu_vest, 0)) * 100, 2) AS \"take_home_pct\" FROM payslip_ingest.payslip WHERE $__timeFilter(pay_date) ORDER BY pay_date",
           "format": "time_series",
           "refId": "A",
           "rawQuery": true,
@@ -540,7 +540,7 @@
           "rawQuery": true,
           "editorMode": "code",
           "format": "table",
-          "rawSql": "SELECT pay_date, employer, tax_year, gross_pay, (gross_pay - rsu_vest) AS cash_gross, rsu_vest, rsu_offset, income_tax, national_insurance, pension_employee, pension_employer, student_loan, COALESCE(other_deductions, '{}'::jsonb) AS other_deductions, net_pay, validated, paperless_doc_id FROM payslip_ingest.payslip WHERE $__timeFilter(pay_date) ORDER BY pay_date DESC"
+          "rawSql": "SELECT pay_date, employer, tax_year, gross_pay, (gross_pay - rsu_vest) AS cash_gross, salary, bonus, rsu_vest, rsu_offset, pension_sacrifice, taxable_pay, income_tax, national_insurance, pension_employee, pension_employer, student_loan, COALESCE(other_deductions, '{}'::jsonb) AS other_deductions, net_pay, validated, paperless_doc_id FROM payslip_ingest.payslip WHERE $__timeFilter(pay_date) ORDER BY pay_date DESC"
         }
       ]
     },
@@ -662,6 +662,250 @@
           "rawSql": "SELECT pay_date AS \"time\", rsu_vest FROM payslip_ingest.payslip WHERE $__timeFilter(pay_date) AND rsu_vest > 0 ORDER BY pay_date"
         }
       ]
+    },
+    {
+      "id": 8,
+      "title": "Earnings breakdown (salary / bonus / RSU / pension sacrifice)",
+      "type": "timeseries",
+      "datasource": {
+        "type": "grafana-postgresql-datasource",
+        "uid": "payslips-pg"
+      },
+      "gridPos": {
+        "h": 9,
+        "w": 12,
+        "x": 0,
+        "y": 49
+      },
+      "fieldConfig": {
+        "defaults": {
+          "custom": {
+            "drawStyle": "bars",
+            "stacking": {
+              "mode": "normal"
+            },
+            "fillOpacity": 80,
+            "lineWidth": 0,
+            "axisCenteredZero": true
+          },
+          "unit": "currencyGBP",
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "options": {
+        "legend": {
+          "showLegend": true,
+          "placement": "bottom"
+        },
+        "tooltip": {
+          "mode": "multi",
+          "sort": "desc"
+        }
+      },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": {
+            "type": "grafana-postgresql-datasource",
+            "uid": "payslips-pg"
+          },
+          "rawQuery": true,
+          "editorMode": "code",
+          "format": "time_series",
+          "rawSql": "SELECT pay_date AS \"time\", salary, bonus, rsu_vest, -pension_sacrifice AS pension_sacrifice FROM payslip_ingest.payslip WHERE $__timeFilter(pay_date) ORDER BY pay_date"
+        }
+      ]
+    },
+    {
+      "id": 9,
+      "title": "Accurate cash effective tax rate (YTD-method vs naive)",
+      "type": "timeseries",
+      "datasource": {
+        "type": "grafana-postgresql-datasource",
+        "uid": "payslips-pg"
+      },
+      "gridPos": {
+        "h": 9,
+        "w": 12,
+        "x": 12,
+        "y": 49
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "unit": "percent",
+          "min": 0,
+          "max": 80,
+          "custom": {
+            "drawStyle": "line",
+            "lineWidth": 2,
+            "fillOpacity": 10
+          },
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "options": {
+        "legend": {
+          "showLegend": true,
+          "placement": "bottom"
+        },
+        "tooltip": {
+          "mode": "multi",
+          "sort": "desc"
+        }
+      },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": {
+            "type": "grafana-postgresql-datasource",
+            "uid": "payslips-pg"
+          },
+          "rawQuery": true,
+          "editorMode": "code",
+          "format": "time_series",
+          "rawSql": "SELECT pay_date AS \"time\", ROUND(((income_tax - (rsu_vest * COALESCE(ytd_tax_paid / NULLIF(ytd_taxable_pay, 0), 0)))::numeric / NULLIF(gross_pay - rsu_vest, 0)) * 100, 2) AS \"cash_tax_rate_ytd\", ROUND((income_tax::numeric / NULLIF(gross_pay, 0)) * 100, 2) AS \"naive_tax_rate\" FROM payslip_ingest.payslip WHERE $__timeFilter(pay_date) ORDER BY pay_date"
+        }
+      ]
+    },
+    {
+      "id": 10,
+      "title": "All-in compensation (cash + RSU market value)",
+      "type": "timeseries",
+      "datasource": {
+        "type": "grafana-postgresql-datasource",
+        "uid": "payslips-pg"
+      },
+      "gridPos": {
+        "h": 9,
+        "w": 12,
+        "x": 0,
+        "y": 58
+      },
+      "fieldConfig": {
+        "defaults": {
+          "custom": {
+            "drawStyle": "bars",
+            "stacking": {
+              "mode": "normal"
+            },
+            "fillOpacity": 80,
+            "lineWidth": 0
+          },
+          "unit": "currencyGBP",
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "blue",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "options": {
+        "legend": {
+          "showLegend": true,
+          "placement": "bottom"
+        },
+        "tooltip": {
+          "mode": "multi",
+          "sort": "desc"
+        }
+      },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": {
+            "type": "grafana-postgresql-datasource",
+            "uid": "payslips-pg"
+          },
+          "rawQuery": true,
+          "editorMode": "code",
+          "format": "time_series",
+          "rawSql": "SELECT pay_date AS \"time\", (gross_pay - rsu_vest) AS cash_gross, rsu_vest FROM payslip_ingest.payslip WHERE $__timeFilter(pay_date) ORDER BY pay_date"
+        }
+      ]
+    },
+    {
+      "id": 11,
+      "title": "YTD cumulative cash gross vs total comp",
+      "type": "timeseries",
+      "datasource": {
+        "type": "grafana-postgresql-datasource",
+        "uid": "payslips-pg"
+      },
+      "gridPos": {
+        "h": 9,
+        "w": 12,
+        "x": 12,
+        "y": 58
+      },
+      "fieldConfig": {
+        "defaults": {
+          "custom": {
+            "drawStyle": "line",
+            "lineWidth": 2,
+            "fillOpacity": 10
+          },
+          "unit": "currencyGBP",
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "options": {
+        "legend": {
+          "showLegend": true,
+          "placement": "bottom"
+        },
+        "tooltip": {
+          "mode": "multi",
+          "sort": "desc"
+        }
+      },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": {
+            "type": "grafana-postgresql-datasource",
+            "uid": "payslips-pg"
+          },
+          "rawQuery": true,
+          "editorMode": "code",
+          "format": "time_series",
+          "rawSql": "SELECT pay_date AS \"time\", SUM(gross_pay - rsu_vest) OVER (PARTITION BY tax_year ORDER BY pay_date) AS ytd_cash_gross, SUM(gross_pay) OVER (PARTITION BY tax_year ORDER BY pay_date) AS ytd_total_comp FROM payslip_ingest.payslip WHERE $__timeFilter(pay_date) ORDER BY pay_date"
+        }
+      ]
     }
   ],
   "refresh": "5m",