feat(metadata): SQLite backend, storage reconciliation and local defaults

- pluggable per-domain Repository interfaces; PostgreSQL and SQLite impls
- SQLite on modernc.org/sqlite (WAL, busy_timeout, foreign_keys, immediate tx)
- separate migrations/sqlite and db.MigrateSQLite; store.NewPostgres/NewSQLite
- cmd/reconcile compares object storage with the journal (report, then --delete)
- storage.Backend.List and photos.Repository.AllStorageKeys
- DB_BACKEND/SQLITE_PATH and STORAGE_BACKEND/FS_ROOT selectable; local defaults
  (sqlite ./galo.db, fs ./data)
- Makefile reconcile/reconcile-delete; docs and .env.example updated

backend/internal/albums/service.go

@@ -18,13 +18,13 @@ type MemberLookup interface {
 }
 
 type Service struct {
-	store   *Store
+	store   Repository
 	members MemberLookup
 	hub     *sse.Hub
 	storage storage.Backend
 }
 
-func NewService(store *Store, members MemberLookup, hub *sse.Hub, storage storage.Backend) *Service {
+func NewService(store Repository, members MemberLookup, hub *sse.Hub, storage storage.Backend) *Service {
 	return &Service{store: store, members: members, hub: hub, storage: storage}
 }