fire-planner: Wave 2 chart-first — flex spending, categorised life

events, interactive Visx Gantt + spending-profile chart

Charts are now the primary editor for life events. The Plan-tab body
re-orders to make charts ~80% of viewport real-estate; legacy form
sections are collapsed into a drawer.

Backend:
- alembic 0004: life_event.category enum (essential / discretionary /
  not_spending). Defaults to essential so existing rows keep their
  full spending impact.
- Simulator gains discretionary_outflows + flex_rules params. Tracks
  per-path running ATH, applies the deepest applicable cut to
  discretionary outflows when portfolio drops vs ATH (PLab-style flex
  spending). Cut amount stays in the portfolio (refund pattern).
- New flex_spending module with FlexRule + applicable_cut +
  cuts_per_year (vectorised). Sortable rules; "deepest cut wins" so
  users specify cumulative cuts at each tier.
- New /scenarios/{id}/spending-profile endpoint returning per-year
  base / essential / discretionary / flex_cut / total breakdown.
- SimulateRequest gains flex_rules + life_event.category roundtrip.
- 8 new tests; 246 total pytest pass; mypy + ruff clean.

Frontend (Visx + ECharts):
- Installed @visx/{scale,shape,group,axis,event,responsive,tooltip}
  for native SVG drag interactions.
- New <SpendingProfileChart> — Visx stacked-area of base/essential/
  discretionary with red flex-cut overlay, hover tooltip, click-to-
  scrub-year.
- New <EventGantt> — interactive Visx Gantt:
    * Click empty space → popover create at that year (default
      essential spending event)
    * Click a bar → inline edit popover (name, kind, range, £/y,
      category) with delete button
    * Drag bar middle → moves the whole event (year-resolution snap)
    * Drag bar edges → resizes year_start / year_end
    * All gestures persist via PATCH /life-events/{id}
- New <FlexRulesEditor> — list of {from_ath_pct, cut} tiers, save-on-
  change to scenario.config_json.flex_rules.
- Plan-tab redesign: NW fan dominant top with floating stat badges
  (Year/Age/NW/Δ NW/Spending/Eff. tax) over the chart; spending-
  profile chart middle; Gantt bottom; flex-rules editor; legacy form
  sections in a collapsed <details> drawer.
- Frontend typecheck + 7 vitest tests + production build all clean.

fire_planner/api/schemas.py

@@ -185,6 +185,9 @@ class AnnualSpending(BaseModel):
 # ── life events ──────────────────────────────────────────────────────
 
 
+_CATEGORY_PATTERN = "^(essential|discretionary|not_spending)$"
+
+
 class LifeEventOut(_Base):
     id: int
     scenario_id: int
@@ -194,6 +197,7 @@ class LifeEventOut(_Base):
     year_end: int | None
     delta_gbp_per_year: Decimal
     one_time_amount_gbp: Decimal | None
+    category: str = "essential"
     enabled: bool
     payload: dict[str, Any] | None
     created_at: datetime
@@ -206,6 +210,7 @@ class LifeEventCreate(BaseModel):
     year_end: int | None = Field(default=None, ge=0, le=100)
     delta_gbp_per_year: Decimal = Decimal("0")
     one_time_amount_gbp: Decimal | None = None
+    category: str = Field(default="essential", pattern=_CATEGORY_PATTERN)
     enabled: bool = True
     payload: dict[str, Any] | None = None
 
@@ -217,6 +222,7 @@ class LifeEventPatch(BaseModel):
     year_end: int | None = None
     delta_gbp_per_year: Decimal | None = None
     one_time_amount_gbp: Decimal | None = None
+    category: str | None = Field(default=None, pattern=_CATEGORY_PATTERN)
     enabled: bool | None = None
     payload: dict[str, Any] | None = None
 
@@ -386,9 +392,46 @@ class LifeEventInput(BaseModel):
     year_end: int | None = Field(default=None, ge=0, le=100)
     delta_gbp_per_year: Decimal = Decimal("0")
     one_time_amount_gbp: Decimal | None = None
+    category: str = Field(default="essential", pattern=_CATEGORY_PATTERN)
     enabled: bool = True
 
 
+class FlexRule(BaseModel):
+    """ProjectionLab-style flex-spending rule.
+
+    When the portfolio falls ``from_ath_pct`` below its running all-time-high,
+    cut discretionary spending by ``cut_discretionary_pct``. Multiple rules
+    stack via "worst applicable threshold wins" — at -30% from ATH a rule
+    keyed at -10% AND a rule keyed at -25% both apply, but only the deeper
+    cut takes effect (so users specify *cumulative* cuts, not per-tier).
+
+    `from_ath_pct` is the absolute drop magnitude as a positive fraction:
+    0.30 means "the portfolio is 30% below its ATH". This matches the way
+    PLab labels its sliders ("if down 30%, cut 60%").
+    """
+    from_ath_pct: Decimal = Field(ge=0, le=1)
+    cut_discretionary_pct: Decimal = Field(ge=0, le=1)
+
+
+# ── spending profile ────────────────────────────────────────────────
+
+
+class SpendingProfilePoint(BaseModel):
+    year_idx: int
+    base_gbp: Decimal
+    essential_gbp: Decimal
+    discretionary_gbp: Decimal
+    not_spending_gbp: Decimal
+    flex_cut_gbp: Decimal
+    total_gbp: Decimal
+
+
+class SpendingProfileResponse(BaseModel):
+    scenario_id: int
+    horizon_years: int
+    points: list[SpendingProfilePoint]
+
+
 class SimulateRequest(BaseModel):
     """Sync, non-persisted simulate. Used by the React UI for what-if.
 
@@ -422,6 +465,7 @@ class SimulateRequest(BaseModel):
     manual_real_return_pct: Decimal | None = None
     income_streams: list[IncomeStreamInput] = Field(default_factory=list)
     goals: list[GoalCreate] = Field(default_factory=list)
+    flex_rules: list[FlexRule] = Field(default_factory=list)
     # Rates settings (Wave 1.D.3). When `rates_mode='fixed'`, the engine
     # synthesises a deterministic real-return path from the per-asset
     # growth + dividend + inflation rates below, weighted by the static