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/application/services/mod.rs

@@ -20,6 +20,7 @@ pub mod magic_link_invite_service;
 pub mod music_service;
 pub mod nextcloud_file_id_service;
 pub mod nextcloud_login_flow_service;
+pub mod places_service;
 pub mod recent_service;
 pub mod recipient_notification_service;
 pub mod search_service;

src/application/services/places_service.rs

@@ -0,0 +1,45 @@
+use std::sync::Arc;
+
+use uuid::Uuid;
+
+use crate::application::dtos::geo_dto::{GeoBounds, GeoCluster};
+use crate::common::errors::DomainError;
+use crate::infrastructure::repositories::pg::FileBlobReadRepository;
+
+/// "Places" use case: the caller's geotagged photos aggregated into map
+/// clusters.
+///
+/// Strictly user-scoped — the repository filters `WHERE fi.user_id = $1`, so,
+/// like [`RecentService`](super::recent_service::RecentService) and the photos
+/// timeline, it needs no `AuthorizationEngine` check: the `caller_id`
+/// parameter *is* the access scope.
+pub struct PlacesService {
+    file_read: Arc<FileBlobReadRepository>,
+}
+
+impl PlacesService {
+    pub fn new(file_read: Arc<FileBlobReadRepository>) -> Self {
+        Self { file_read }
+    }
+
+    /// Aggregation cell side, in degrees, for a slippy-map zoom level. The
+    /// world (360°) is split into `2^zoom` tiles; we use ~4 cells per tile so
+    /// clusters refine as the user zooms in. Clamped to a sane range.
+    fn cell_for_zoom(zoom: u8) -> f64 {
+        let z = i32::from(zoom.min(20));
+        360.0 / (2_f64.powi(z) * 4.0)
+    }
+
+    /// Clustered geotagged photos for `caller_id` within `bounds`.
+    pub async fn clusters(
+        &self,
+        caller_id: Uuid,
+        bounds: GeoBounds,
+        zoom: u8,
+    ) -> Result<Vec<GeoCluster>, DomainError> {
+        let cell = Self::cell_for_zoom(zoom);
+        self.file_read
+            .list_geo_clusters(caller_id, bounds, cell)
+            .await
+    }
+}