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>

apps/planner/app/components/PlannerMap.tsx

@@ -29,7 +29,7 @@ import { useGpxDrop } from "~/lib/use-gpx-drop";
 import { useNearbyPois } from "~/lib/use-nearby-pois";
 import { NearbyPoiMarkers } from "./NearbyPoiMarkers";
 import { poiCategories } from "@trails-cool/map-core";
-import type { Poi } from "~/lib/overpass";
+import type { Poi } from "~/lib/pois";
 import "leaflet/dist/leaflet.css";
 
 function waypointIcon(index: number, overnight?: boolean, highlighted?: boolean, hasNote?: boolean): L.DivIcon {