poi-index: map-core selectors, planner.pois schema, /api/pois route + client, metrics

Replace the planner's Overpass proxy with a self-hosted POI index:
- map-core POI categories become structured tag selectors (single source of
  truth) + osmium filter / classification helpers
- planner.pois PostGIS table (centroid points, GiST + category indexes)
- /api/pois serving route (session + same-origin + rate limit, 100 cap)
- lib/pois.ts client (renamed from overpass.ts; GET, quantized bbox)
- metrics: poi_api_requests_total + DB-collected index rows/age gauges;
  drop overpass_* metrics
- remove /api/overpass proxy + dead OVERPASS_URLS on the planner service
  (Journal surface backfill still uses it via code default)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

infrastructure/.env.example

@@ -11,9 +11,11 @@ SESSION_SECRET=change-me
 S3_ACCESS_KEY=
 S3_SECRET_KEY=
 
-# Overpass upstream failover. Comma-separated list tried in order;
-# first 2xx response wins. Falls back to the single-URL OVERPASS_URL
-# if this is unset, and to a built-in default list if neither is set.
+# Overpass upstream failover for the Journal's surface-breakdown backfill
+# (route-surface-breakdown). Comma-separated list tried in order; first 2xx
+# response wins. Falls back to the single-URL OVERPASS_URL if unset, and to a
+# built-in default list if neither is set. The Planner no longer uses Overpass
+# — its POI overlays are served from the self-hosted `planner.pois` index.
 # OVERPASS_URLS=https://lz4.overpass-api.de/api/interpreter,https://overpass-api.de/api/interpreter
 
 # Demo-activity-bot. Only enable in prod. When true, the journal worker