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/common/config.rs

@@ -879,6 +879,8 @@ pub struct FeaturesConfig {
     pub enable_trash: bool,
     pub enable_search: bool,
     pub enable_music: bool,
+    /// Lists the user's geotagged photos on a map (GET /api/photos/geo).
+    pub enable_places: bool,
     /// Expose other OxiCloud users as a read-only "system" address book
     /// at GET /api/address-books. Set to false to hide the user directory.
     pub expose_system_users: bool,
@@ -893,6 +895,7 @@ impl Default for FeaturesConfig {
             enable_trash: true,        // Enable trash feature
             enable_search: true,       // Enable search feature
             enable_music: true,        // Enable music feature
+            enable_places: false,      // Photo map; off until the map UI ships
             expose_system_users: true, // Expose OxiCloud users as address book by default
         }
     }
@@ -1378,6 +1381,12 @@ impl AppConfig {
             config.features.enable_music = val;
         }
 
+        if let Ok(enable_places) = env::var("OXICLOUD_ENABLE_PLACES").map(|v| v.parse::<bool>())
+            && let Ok(val) = enable_places
+        {
+            config.features.enable_places = val;
+        }
+
         // Content search (embedded Tantivy index)
         if let Ok(v) = env::var("OXICLOUD_ENABLE_CONTENT_SEARCH").map(|v| v.parse::<bool>())
             && let Ok(val) = v