feat: map view with GPS extraction fix

Adds a new Map sidebar entry that plots photos by their EXIF GPS
coordinates on a clustered Leaflet map. While wiring this up, the
metadata extractor was reading unprefixed GPS keys that never exist
in `exiftool -G -j` output AND assumed coordinates were already
floats — every photo silently lost its GPS. The new extract_gps
helper handles Composite/EXIF group prefixes and parses DMS strings,
and lat/lon are stored as first-class indexed columns so the map
can query them without parsing exif_json on every request.

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

frontend/src/services/api.ts

@@ -97,6 +97,20 @@ export const photos = {
     return response.data
   },
 
+  /** Lightweight list of every photo with GPS coordinates, used by the
+   *  Map view. Returns one tiny object per photo (id, lat, lon, taken_at)
+   *  rather than the full photo payload — keeps responses small even on
+   *  big libraries. */
+  mapPoints: async () => {
+    const response = await api.get('/photos/map')
+    return response.data as Array<{
+      id: string
+      latitude: number
+      longitude: number
+      taken_at: string | null
+    }>
+  },
+
   update: async (photoId: string, data: {
     filename?: string
     rating?: number
@@ -410,6 +424,7 @@ export interface LibraryStats {
   all_photos: number
   rated: number
   colored: number
+  with_gps: number
   duplicates: number
   discarded: number
   total_photos: number