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/app/objects_test.go

@@ -15,6 +15,7 @@ import (
 	"shared-album/internal/config"
 	"shared-album/internal/sse"
 	"shared-album/internal/storage"
+	"shared-album/internal/store"
 )
 
 func newTestServerWithFS(t *testing.T) (*storage.FS, *gin.Engine) {
@@ -28,7 +29,8 @@ func newTestServerWithFS(t *testing.T) (*storage.FS, *gin.Engine) {
 	if err != nil {
 		t.Fatalf("new fs: %v", err)
 	}
-	srv := New(&config.Config{}, nil, fs, sse.NewHub(1))
+	noop := func(context.Context) error { return nil }
+	srv := New(&config.Config{}, store.Repos{}, noop, fs, sse.NewHub(1))
 	return fs, srv.Router()
 }