feat: unified photo provider abstraction layer (#584)

Introduce trek_photos as central photo registry. Frontend uses
/api/photos/:id/:kind instead of provider-specific URLs. Adding
a new photo provider is now backend-only work.

- New trek_photos table (migration 98) with photo_id FK in
  trip_photos and journey_photos
- Unified /api/photos/:id/thumbnail|original|info endpoint
- photoResolverService for central resolution and streaming
- ProviderPicker: add "All Photos" tab, rename tabs, fix i18n
- Localize all hardcoded strings in JourneyDetailPage (14 langs)
- Fix date formatting to use browser locale instead of hardcoded 'en'
- Journey stats as styled tile cards

client/src/store/journeyStore.ts

@@ -42,17 +42,19 @@ export interface JourneyEntry {
 export interface JourneyPhoto {
   id: number
   entry_id: number
-  provider: 'local' | 'immich' | 'synologyphotos'
+  photo_id: number
+  caption?: string | null
+  sort_order: number
+  shared: number
+  created_at: number
+  // Joined from trek_photos for display
+  provider?: string
   asset_id?: string | null
   owner_id?: number | null
   file_path?: string | null
   thumbnail_path?: string | null
-  caption?: string | null
-  sort_order: number
   width?: number | null
   height?: number | null
-  shared: number
-  created_at: number
 }
 
 export interface JourneyTrip {