- Add /api/activity/{id}/geojson and /api/activity/{id}/timeseries endpoints
(bearer-token-gated, falls back from _merged to raw activities dir)
- Rewrite activity detail screen with MapLibreGL v11 API (Map, Camera,
GeoJSONSource, Layer) and react-native-svg area chart with gradient fill
- On-demand fetch for remote activities that have no local geojson/timeseries
- Add react-native-svg dependency; requires dev build (npx expo run:android)