feat: map view with GPS extraction fix

Adds a new Map sidebar entry that plots photos by their EXIF GPS
coordinates on a clustered Leaflet map. While wiring this up, the
metadata extractor was reading unprefixed GPS keys that never exist
in `exiftool -G -j` output AND assumed coordinates were already
floats — every photo silently lost its GPS. The new extract_gps
helper handles Composite/EXIF group prefixes and parses DMS strings,
and lat/lon are stored as first-class indexed columns so the map
can query them without parsing exif_json on every request.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/routers/library.py

@@ -62,6 +62,14 @@ async def get_library_stats(db: AsyncSession = Depends(get_db)):
         )
     ).scalar() or 0
 
+    with_gps_count = (
+        await db.execute(
+            select(func.count(Photo.id)).where(
+                not_discarded, Photo.latitude.is_not(None)
+            )
+        )
+    ).scalar() or 0
+
     duplicates_count = (
         await db.execute(
             select(func.count(Photo.id)).where(
@@ -96,6 +104,7 @@ async def get_library_stats(db: AsyncSession = Depends(get_db)):
         "all_photos": all_photos_count,
         "rated": rated_count,
         "colored": colored_count,
+        "with_gps": with_gps_count,
         "duplicates": duplicates_count,
         "discarded": discarded_count,
         "total_photos": photo_count,
@@ -108,11 +117,23 @@ async def get_library_stats(db: AsyncSession = Depends(get_db)):
 async def trigger_scan():
     """Trigger full library re-scan"""
     from app.tasks.scan import scan_all_source_roots
-    
+
     scan_all_source_roots.delay()
-    
+
     return {"status": "success", "message": "Library scan started"}
 
+
+@router.post("/backfill-gps")
+async def trigger_backfill_gps():
+    """Re-run EXIF metadata extraction on every photo that's still missing
+    GPS coordinates. Useful after fixing the EXIF parser, or any time the
+    Map view looks emptier than expected. Returns immediately — work runs
+    on the Celery worker."""
+    from app.tasks.scan import backfill_gps
+
+    backfill_gps.delay()
+    return {"status": "success", "message": "GPS backfill queued"}
+
 @router.get("/scan/status")
 async def get_scan_status(db: AsyncSession = Depends(get_db)):
     """Get current scan status"""