Add POI overlay panel, markers, and map integration

- PoiPanel: Collapsible panel with category checkboxes, count badges,
  loading/error/zoom-too-low states
- PoiMarkers: L.Marker with L.DivIcon per POI, click popup with name,
  hours, website, OSM link. z-index below route/waypoints.
- PoiRefresher: Listens to map moveend, refreshes POIs via usePois hook
- Wired into PlannerMap alongside existing controls

Skipped markercluster (7.3) — can add later if density is an issue.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/planner/app/lib/use-pois.ts

@@ -1,7 +1,7 @@
 import { useCallback, useEffect, useRef, useState } from "react";
 import { queryPois, OverpassRateLimitError, type Poi, type BBox } from "./overpass.ts";
 import { getCached, setCached } from "./poi-cache.ts";
-import { poiCategories, type PoiCategory } from "./poi-categories.ts";
+import { poiCategories } from "./poi-categories.ts";
 
 const MIN_ZOOM = 12;
 const DEBOUNCE_MS = 500;