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/infrastructure/repositories/pg/file_blob_read_repository.rs

@@ -32,6 +32,7 @@ use std::pin::Pin;
 use std::sync::Arc;
 use std::time::Duration;
 
+use crate::application::dtos::geo_dto::{GeoBounds, GeoCluster};
 use crate::application::dtos::search_dto::SearchCriteriaDto;
 use crate::application::ports::storage_ports::FileReadPort;
 use crate::common::errors::DomainError;
@@ -416,6 +417,56 @@ impl FileBlobReadRepository {
 
         Ok((files, sort_dates, dims))
     }
+
+    /// Aggregate the caller's geotagged photos into grid cells of side `cell`
+    /// (degrees) within `bounds`. Plain SQL (no PostGIS), scoped to `user_id`.
+    /// Returns one cluster per non-empty cell with its centroid, photo count
+    /// and a representative photo id (for the cluster thumbnail).
+    pub async fn list_geo_clusters(
+        &self,
+        user_id: Uuid,
+        bounds: GeoBounds,
+        cell: f64,
+    ) -> Result<Vec<GeoCluster>, DomainError> {
+        let rows: Vec<(i64, f64, f64, String)> = sqlx::query_as(
+            r#"
+            SELECT count(*)              AS n,
+                   avg(fm.longitude)     AS clng,
+                   avg(fm.latitude)      AS clat,
+                   min(fm.file_id::text) AS sample_id
+              FROM storage.file_metadata fm
+              JOIN storage.files fi ON fi.id = fm.file_id
+             WHERE fi.user_id = $1
+               AND NOT fi.is_trashed
+               AND fm.latitude IS NOT NULL
+               AND fm.longitude IS NOT NULL
+               AND fm.longitude BETWEEN $2 AND $3
+               AND fm.latitude  BETWEEN $4 AND $5
+             GROUP BY round(fm.longitude / $6), round(fm.latitude / $6)
+            "#,
+        )
+        .bind(user_id)
+        .bind(bounds.west)
+        .bind(bounds.east)
+        .bind(bounds.south)
+        .bind(bounds.north)
+        .bind(cell)
+        .fetch_all(self.pool.as_ref())
+        .await
+        .map_err(|e| {
+            DomainError::internal_error("FileBlobRead", format!("list_geo_clusters: {e}"))
+        })?;
+
+        Ok(rows
+            .into_iter()
+            .map(|(n, clng, clat, sample_id)| GeoCluster {
+                lng: clng,
+                lat: clat,
+                count: n,
+                sample_file_id: sample_id,
+            })
+            .collect())
+    }
 }
 
 impl FileReadPort for FileBlobReadRepository {