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/fs_test.go

@@ -172,3 +172,33 @@ func TestContentTypeForKey(t *testing.T) {
 		}
 	}
 }
+
+func TestFSList(t *testing.T) {
+	ctx := context.Background()
+	fs := newTestFS(t)
+	for _, key := range []string{"objects/a/original.jpg", "objects/b/original.jpg", "misc/readme.txt"} {
+		if err := fs.Put(ctx, key, strings.NewReader("x"), 1, "text/plain"); err != nil {
+			t.Fatalf("put %s: %v", key, err)
+		}
+	}
+
+	all, err := fs.List(ctx, "")
+	if err != nil || len(all) != 3 {
+		t.Fatalf("list all: %v len=%d", err, len(all))
+	}
+	objs, err := fs.List(ctx, "objects/")
+	if err != nil {
+		t.Fatalf("list objects: %v", err)
+	}
+	if len(objs) != 2 {
+		t.Fatalf("list objects len=%d, want 2", len(objs))
+	}
+	for _, o := range objs {
+		if !strings.HasPrefix(o.Key, "objects/") {
+			t.Fatalf("unexpected key %q", o.Key)
+		}
+		if o.Size != 1 || o.ModTime.IsZero() {
+			t.Fatalf("unexpected info %+v", o)
+		}
+	}
+}