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/mod.rs

@@ -164,6 +164,7 @@ use crate::interfaces::api::handlers::file_handler::MoveFilePayload;
         handlers::recent_handler::clear_recent_items,
         // Photos handler (free function)
         handlers::photos_handler::list_photos,
+        handlers::photos_handler::list_photos_geo,
         // Batch handlers (free functions)
         handlers::batch_handler::move_files_batch,
         handlers::batch_handler::copy_files_batch,