feat: journey gallery 1-to-N model with M:N entry-photo junction table

Replaces the old model where journey_photos was keyed per-entry with a
per-journey gallery table (one row per unique photo per journey) and a new
junction table journey_entry_photos that links gallery photos to entries.

Key changes:
- Migration 121: renames old journey_photos to journey_photos_old, creates the
  new gallery table + junction table, backfills both from existing data, drops
  the backup, removes synthetic 'Gallery' / '[Trip Photos]' wrapper entries
- journeyService: rewrites photo helpers (JP_SELECT/JOIN now joins via
  journey_entry_photos → journey_photos → trek_photos); adds uploadGalleryPhotos,
  addProviderPhotoToGallery, unlinkPhotoFromEntry, deleteGalleryPhoto; simplifies
  deletePhoto and linkPhotoToEntry against the new schema; syncTripPhotos inserts
  directly into the gallery instead of a wrapper entry
- journeyShareService: updates public photo and asset validation queries to join
  through the gallery table instead of entry_id; getPublicJourney now returns a
  dedicated gallery array alongside per-entry photos
- journey routes: adds gallery upload, provider-photo, and delete endpoints
  (POST/DELETE /:id/gallery/*); adds unlink-from-entry route
  (DELETE /entries/:entryId/photos/:journeyPhotoId); updates link-photo to
  accept journey_photo_id with a backwards-compat photo_id alias
- types: adds GalleryPhoto interface
- client api: adds uploadGalleryPhotos, addProviderPhotosToGallery, unlinkPhoto,
  deleteGalleryPhoto; updates linkPhoto param name to journeyPhotoId
- journeyStore: adds GalleryPhoto type, gallery field on JourneyDetail,
  uploadGalleryPhotos / unlinkPhoto / deleteGalleryPhoto store actions
- JourneyDetailPage + tests: updated to work with the new gallery model

server/src/types.ts

@@ -389,6 +389,24 @@ export interface JourneyPhoto {
   height?: number | null;
 }
 
+export interface GalleryPhoto {
+  id: number;
+  journey_id: number;
+  photo_id: number;
+  caption?: string | null;
+  shared: number;
+  sort_order: number;
+  created_at: number;
+  // Joined from trek_photos for API responses
+  provider?: string;
+  asset_id?: string | null;
+  owner_id?: number | null;
+  file_path?: string | null;
+  thumbnail_path?: string | null;
+  width?: number | null;
+  height?: number | null;
+}
+
 export interface JourneyTrip {
   journey_id: number;
   trip_id: number;