Add EXIF search infrastructure (Phase 1 & 2)

Implements foundation for EXIF-based photo search capabilities:

- Add geo.rs module with GPS distance calculations (Haversine + bounding box)
- Extend FilesRequest with EXIF search parameters (camera, GPS, date, media type)
- Add MediaType enum and DateTakenAsc/DateTakenDesc sort options
- Create date_taken index migration for efficient date queries
- Implement ExifDao methods: get_exif_batch, query_by_exif, get_camera_makes
- Add FileWithMetadata struct for date-aware sorting
- Implement date sorting with filename extraction fallback
- Make extract_date_from_filename public for reuse

Next: Integrate EXIF filtering into list_photos() and enhance get_all_tags()

migrations/2025-12-18-120000_add_date_taken_index/up.sql

@@ -0,0 +1,2 @@
+-- Add index on date_taken for efficient date range queries
+CREATE INDEX IF NOT EXISTS idx_image_exif_date_taken ON image_exif(date_taken);