Add per-waypoint notes and nearby POI snap to Planner

- `note` field on Waypoint type, stored in Yjs Y.Map and exported as
  `<desc>` inside `<wpt>` in GPX
- Inline textarea note editing in WaypointSidebar with auto-resize,
  character counter (500 max), save-on-blur, Escape cancel
- Note indicator dot on map markers; note tooltip on hover
- `useNearbyPois` hook: fetches POIs within 500m of selected waypoint
  via Overpass proxy, 500ms debounce, AbortController, 60s rate-limit
  suppression
- NearbyPoiMarkers component: renders POI markers on map for selected
  waypoint with snap-to-POI on click
- Nearby section in WaypointSidebar: list with snap buttons, spinner,
  empty/rate-limited states, "Show more" toggle (5 → all)
- Unit tests for fetchNearbyPois bbox geometry and snap-to-POI Yjs
  transaction behaviour

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/types/src/index.ts

@@ -21,6 +21,7 @@ export interface Waypoint {
   lat: number;
   lon: number;
   name?: string;
+  note?: string;
   isDayBreak?: boolean;
   osmId?: number;
   poiTags?: WaypointPoiTags;