feat(fire-target): per-Case FIRE-number solver for the retirement countdown

Add a Monte-Carlo "FIRE number" solver so the wealth dashboard can show a £
countdown to retirement across life-stage cases, in today's money.

Viktor wants to see, per country, how far his net worth is from being able to
retire for good under three cases — Solo (his spend ×1.5), Household (+Anca
×1.5), Family (+2 kids) — with cost-of-living re-scaling per country and a 99%
Guyton-Klinger success bar.

- spend_model: per-Case real-GBP spend, COL-scaled (rent + non-rent essentials
  scale by country; Holidays fixed), ×1.5 safety. Constants sourced live from
  actualbudget (Viktor) / on-record (Anca).
- geo: city -> tax jurisdiction (nomad fallback).
- fire_target: binary-search the smallest LIQUID net worth where GK reaches the
  bar; pension modelled as a tranche unlocking at ~57, kids ramp + optional home
  as cashflows. New fire_target table (migration 0007) + idempotent upsert.
- recompute-fire-targets CLI: solve every Case x country and persist for Grafana.
- CONTEXT.md glossary + ADR-0001 (why MC-threshold on liquid NW, not 25x spend).

Reuses the existing simulator unchanged (its cashflow hooks already supported
pension/kids/home). 345 tests pass; mypy + ruff clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_geo.py

@@ -0,0 +1,37 @@
+"""City -> tax jurisdiction mapping for the countdown solver."""
+from __future__ import annotations
+
+import pytest
+
+from fire_planner.geo import jurisdiction_for_city
+
+
+@pytest.mark.parametrize(
+    ("slug", "expected"),
+    [
+        ("sofia", "bulgaria"),
+        ("limassol", "cyprus"),
+        ("bangkok", "thailand"),
+        ("chiang-mai", "thailand"),
+        ("kuala-lumpur", "malaysia"),
+        ("penang", "malaysia"),
+        ("dubai", "uae"),
+        ("london", "uk"),
+    ],
+)
+def test_known_cities_map_to_their_regime(slug: str, expected: str) -> None:
+    assert jurisdiction_for_city(slug) == expected
+
+
+@pytest.mark.parametrize("slug", ["lisbon", "porto", "athens", "tbilisi", "atlantis", ""])
+def test_unmapped_cities_fall_back_to_nomad(slug: str) -> None:
+    assert jurisdiction_for_city(slug) == "nomad"
+
+
+def test_mapping_only_uses_regimes_the_engine_knows() -> None:
+    from fire_planner.geo import CITY_JURISDICTION
+    from fire_planner.scenarios import _JURISDICTION_CONSTRUCTORS
+
+    known = set(_JURISDICTION_CONSTRUCTORS)
+    assert set(CITY_JURISDICTION.values()) <= known
+    assert "nomad" in known