Security fix: Implement Google Maps API photo proxy (Fix 3)

Completed HIGH severity security fix (CVSS 6.5) to prevent Google Maps
API key exposure to frontend clients.

Issue: API key was embedded in photo URLs sent to frontend, allowing
potential abuse and quota exhaustion.

Solution: Implemented backend proxy endpoint for photos.

Backend Changes:
- google-maps.client.ts: Changed photoUrl to photoReference, added fetchPhoto()
- stations.types.ts: Updated type definition (photoUrl → photoReference)
- stations.controller.ts: Added getStationPhoto() proxy method
- stations.routes.ts: Added GET /api/stations/photo/:reference route
- stations.service.ts: Updated to use photoReference
- stations.repository.ts: Updated database queries and mappings
- admin controllers/services: Updated for consistency
- Created migration 003 to rename photo_url column

Frontend Changes:
- stations.types.ts: Updated type definition (photoUrl → photoReference)
- photo-utils.ts: NEW - Helper to generate proxy URLs
- StationCard.tsx: Use photoReference with helper function

Tests & Docs:
- Updated mock data to use photoReference
- Updated test expectations for proxy URLs
- Updated API.md and TESTING.md documentation

Database Migration:
- 003_rename_photo_url_to_photo_reference.sql: Renames column in station_cache

Security Benefits:
- API key never sent to frontend
- All photo requests proxied through authenticated endpoint
- Photos cached for 24 hours (Cache-Control header)
- No client-side API key exposure

Files modified: 16 files
New files: 2 (photo-utils.ts, migration 003)

Status: All 3 P0 security fixes now complete
- Fix 1: crypto.randomBytes() ✓
- Fix 2: Magic byte validation ✓
- Fix 3: API key proxy ✓

Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

backend/src/features/admin/api/stations.controller.ts

@@ -23,7 +23,7 @@ interface CreateStationBody {
   pricePremium?: number;
   priceDiesel?: number;
   rating?: number;
-  photoUrl?: string;
+  photoReference?: string;
 }
 
 interface UpdateStationBody {
@@ -35,7 +35,7 @@ interface UpdateStationBody {
   pricePremium?: number;
   priceDiesel?: number;
   rating?: number;
-  photoUrl?: string;
+  photoReference?: string;
 }
 
 interface StationParams {