col: simulator auto-adjusts spending to local prices via Numbeo+Expatistan

The Monte Carlo used to compare jurisdictions at a flat London-equivalent
spend, which silently overstated the cost-of-living for any move to a
cheaper region. Now every cross-jurisdiction simulation auto-scales
spending_gbp by the real Numbeo/Expatistan ratio between the user's
baseline city and the target city.

Architecture:
- fire_planner/col/baseline.py — 22 cities with headline Numbeo data
  (source URLs + snapshot dates embedded) — fallback when scraper fails
- col/numbeo.py + col/expatistan.py — httpx async scrapers, regex-parsed,
  polite 1.1s rate-limit, EUR/USD anchored
- col/cache.py — PG-backed cache (col_snapshot table, 1-year TTL)
- col/service.py — sync compute_col_ratio() for the simulator; async
  lookup_city_cached() with source reconciliation for the refresh CronJob
- alembic 0005 — col_snapshot table, UNIQUE(city_slug, source_name)

Simulator wiring:
- SimulateRequest gains col_auto_adjust=True (default), col_baseline_city,
  col_target_city. Defaults pick the jurisdiction's representative city.
- _resolve_col_adjustment scales spending_gbp before path-building.
- SimulateResult surfaces col_multiplier_applied + col_adjusted_spending_gbp.

CLIs:
- python -m fire_planner col-seed — loads BASELINES into col_snapshot
  (post-migration seed step)
- python -m fire_planner col-refresh-stale --within-days 7 — used by the
  weekly fire-planner-col-refresh CronJob

268 tests pass. Mypy strict + ruff clean.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

alembic/versions/0005_col_snapshot.py

@@ -0,0 +1,73 @@
+"""add col_snapshot table for cached cost-of-living data
+
+Revision ID: 0005
+Revises: 0004
+Create Date: 2026-05-21 12:00:00.000000
+
+Phase 2 of the cost-of-living subsystem (`fire_planner.col`). Caches
+Numbeo / Expatistan headline data with a 1-year TTL so the simulator
+can scale `spending_gbp` to local prices without re-scraping per-call.
+Refresh is async (Phase-3 CronJob); user-facing lookups never block on
+the network in the steady state.
+
+Unique on (city_slug, source_name) — multiple sources per city are
+allowed; service.py reconciles them when computing the headline.
+"""
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+
+from alembic import op
+
+revision: str = "0005"
+down_revision: str | None = "0004"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+SCHEMA = "fire_planner"
+
+
+def upgrade() -> None:
+    op.create_table(
+        "col_snapshot",
+        sa.Column("id", sa.Integer(), nullable=False, autoincrement=True),
+        sa.Column("city_slug", sa.String(length=64), nullable=False),
+        sa.Column("city_display", sa.String(length=128), nullable=False),
+        sa.Column("country", sa.String(length=64), nullable=False),
+        sa.Column("source_name", sa.String(length=32), nullable=False),
+        sa.Column("source_url", sa.String(), nullable=True),
+        sa.Column("snapshot_date", sa.Date(), nullable=False),
+        sa.Column("fetched_at", sa.TIMESTAMP(timezone=True), nullable=False,
+                  server_default=sa.func.now()),
+        sa.Column("expires_at", sa.TIMESTAMP(timezone=True), nullable=False),
+        sa.Column("total_no_rent_gbp", sa.Numeric(12, 2), nullable=False),
+        sa.Column("total_with_rent_gbp", sa.Numeric(12, 2), nullable=False),
+        sa.Column("rent_1bed_center_gbp", sa.Numeric(12, 2), nullable=False),
+        sa.Column("rent_1bed_outside_gbp", sa.Numeric(12, 2), nullable=True),
+        sa.Column("raw_currency", sa.String(length=3), nullable=False,
+                  server_default=sa.text("'GBP'")),
+        sa.Column("gbp_per_unit", sa.Numeric(12, 8), nullable=False,
+                  server_default=sa.text("1")),
+        sa.Column("by_category_json", sa.JSON(), nullable=True),
+        sa.PrimaryKeyConstraint("id"),
+        sa.UniqueConstraint("city_slug", "source_name", name="uq_col_snapshot_city_source"),
+        schema=SCHEMA,
+    )
+    op.create_index(
+        "ix_col_snapshot_city_slug",
+        "col_snapshot",
+        ["city_slug"],
+        schema=SCHEMA,
+    )
+    op.create_index(
+        "ix_col_snapshot_expires_at",
+        "col_snapshot",
+        ["expires_at"],
+        schema=SCHEMA,
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_col_snapshot_expires_at", table_name="col_snapshot", schema=SCHEMA)
+    op.drop_index("ix_col_snapshot_city_slug", table_name="col_snapshot", schema=SCHEMA)
+    op.drop_table("col_snapshot", schema=SCHEMA)