feat(places): backend for the photo map (geo clusters API)

Phase 1 server side, gated on OXICLOUD_ENABLE_PLACES (off by default):

- migration: partial index on storage.file_metadata(longitude, latitude).
- FileBlobReadRepository::list_geo_clusters — plain-SQL grid aggregation
  (no PostGIS) scoped to the caller's own non-trashed photos, returning a
  centroid, count and a representative file id per non-empty cell.
- PlacesService (caller_id-scoped; user-scoped data needs no authz check,
  mirroring RecentService) with a zoom→cell-size mapping.
- GET /api/photos/geo?bbox=w,s,e,n&zoom=N returning GeoCluster[]. The route
  is mounted only when the Places service is present, and is registered in
  the OpenAPI path list.

The map frontend (PMTiles serving + MapLibre module) is deferred pending
the basemap-sourcing and vendoring decision.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JW6ghFMDtnRYuYNzZhb47M

src/interfaces/api/routes.rs

@@ -431,9 +431,11 @@ pub fn create_api_routes(app_state: &Arc<AppState>) -> Router<Arc<AppState>> {
     {
         use crate::interfaces::api::handlers::photos_handler;
 
-        let photos_router = Router::new()
-            .route("/", get(photos_handler::list_photos))
-            .with_state(app_state.clone());
+        let mut photos_router = Router::new().route("/", get(photos_handler::list_photos));
+        if app_state.places_service.is_some() {
+            photos_router = photos_router.route("/geo", get(photos_handler::list_photos_geo));
+        }
+        let photos_router = photos_router.with_state(app_state.clone());
 
         router = router.nest("/photos", photos_router);
     }