fire-planner: lazy-refresh /networth from wf_sync (default TTL 1d)

The account_snapshot cache fed /networth, /networth/history, and
/scenarios/{id}/progress. No CronJob populated it, so the cache had
drifted ~18 days behind the wealthfolio_sync mirror (last refresh
2026-05-09 via manual kubectl exec; Grafana reads wf_sync directly
and stayed fresh).

Switch to lazy refresh on read: each request to those endpoints now
checks MAX(account_snapshot.snapshot_date) — if it's older than
NETWORTH_CACHE_TTL_DAYS (default 1), pull fresh rows from wf_sync via
read_account_snapshots_from_pg and upsert. Idempotent under
concurrency (existing ON CONFLICT DO UPDATE).

Plumbing:
- Add get_wf_sync_session dependency that yields None when the wf_sync
  factory isn't wired (keeps existing tests' behaviour: no refresh
  attempted, they continue to seed account_snapshot directly).
- Wire wf_sync engine + session_factory in app.lifespan when
  WEALTHFOLIO_SYNC_DB_CONNECTION_STRING is set.
- Centralise the staleness check in refresh_account_snapshots_if_stale.

Tests:
- 271 existing tests still green.
- Three new tests in test_api_networth_refresh.py covering: empty cache
  triggers refresh, stale cache triggers refresh, fresh cache skips
  refresh (asserts the wf_sync value is NOT served).

fire_planner/api/networth.py

@@ -1,7 +1,8 @@
 """Net-worth read endpoints.
 
-Reads from `fire_planner.account_snapshot` (populated hourly by the
-wealthfolio ingest). Two views:
+Reads from `fire_planner.account_snapshot`, which is lazily refreshed
+from the wealthfolio_sync PG mirror on each request when older than
+`NETWORTH_CACHE_TTL_DAYS` (default 1). Two views:
 - GET /networth          → latest snapshot per account, totals
 - GET /networth/history  → daily totals + per-account series, for charts
 """
@@ -15,7 +16,7 @@ from fastapi import APIRouter, Depends, Query
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from fire_planner.api.dependencies import get_session
+from fire_planner.api.dependencies import get_session, get_wf_sync_session
 from fire_planner.api.schemas import (
     AccountSnapshotOut,
     NetWorthCurrent,
@@ -23,13 +24,18 @@ from fire_planner.api.schemas import (
     NetWorthHistoryPoint,
 )
 from fire_planner.db import AccountSnapshot
+from fire_planner.ingest.wealthfolio import refresh_account_snapshots_if_stale
 
 router = APIRouter(prefix="/networth", tags=["networth"])
 
 
 @router.get("", response_model=NetWorthCurrent)
-async def current_networth(session: AsyncSession = Depends(get_session)) -> NetWorthCurrent:
+async def current_networth(
+    session: AsyncSession = Depends(get_session),
+    wf_sync: AsyncSession | None = Depends(get_wf_sync_session),
+) -> NetWorthCurrent:
     """Latest snapshot per account + GBP total."""
+    await refresh_account_snapshots_if_stale(session, wf_sync)
     latest_date = (await session.execute(
         select(AccountSnapshot.snapshot_date).order_by(
             AccountSnapshot.snapshot_date.desc()).limit(1))).scalar()
@@ -46,6 +52,7 @@ async def current_networth(session: AsyncSession = Depends(get_session)) -> NetW
 @router.get("/history", response_model=NetWorthHistory)
 async def networth_history(
     session: AsyncSession = Depends(get_session),
+    wf_sync: AsyncSession | None = Depends(get_wf_sync_session),
     days: int = Query(default=365, ge=1, le=3650, description="Look-back window."),
 ) -> NetWorthHistory:
     """Daily NW total + per-account breakdown for a stacked area chart.
@@ -53,6 +60,7 @@ async def networth_history(
     Picks one row per (account_id, snapshot_date) — wealthfolio ingest
     upserts daily so this is already de-duped, but we group defensively.
     """
+    await refresh_account_snapshots_if_stale(session, wf_sync)
     rows = (await session.execute(
         select(
             AccountSnapshot.snapshot_date,