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/storage/s3_test.go

@@ -117,6 +117,33 @@ func TestS3ServeObject(t *testing.T) {
 	})
 }
 
+func TestS3List(t *testing.T) {
+	ctx := context.Background()
+	cl, _ := newTestS3(t)
+	prefix := "objects/" + strconv.FormatInt(time.Now().UnixNano(), 10) + "/"
+	keys := []string{prefix + "original.jpg", prefix + "thumb.webp"}
+	for _, k := range keys {
+		if err := cl.Put(ctx, k, strings.NewReader("x"), 1, "image/jpeg"); err != nil {
+			t.Fatalf("put %s: %v", k, err)
+		}
+	}
+	t.Cleanup(func() { _ = cl.Delete(context.Background(), keys...) })
+
+	got, err := cl.List(ctx, prefix)
+	if err != nil {
+		t.Fatalf("list: %v", err)
+	}
+	found := map[string]bool{}
+	for _, o := range got {
+		found[o.Key] = true
+	}
+	for _, k := range keys {
+		if !found[k] {
+			t.Fatalf("key %s not listed: %+v", k, got)
+		}
+	}
+}
+
 func TestS3ServeObjectHead(t *testing.T) {
 	ctx := context.Background()
 	cl, signer := newTestS3(t)