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/store/store_test.go

@@ -0,0 +1,55 @@
+package store
+
+import (
+	"context"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+
+	assets "shared-album"
+	"shared-album/internal/db"
+)
+
+func assertComplete(t *testing.T, r Repos) {
+	t.Helper()
+	if r.Auth == nil || r.Albums == nil || r.Members == nil || r.Photos == nil ||
+		r.Social == nil || r.Notifications == nil || r.ShareLinks == nil {
+		t.Fatalf("incomplete repository bundle: %+v", r)
+	}
+}
+
+func TestNewSQLite(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "meta.db")
+	migFS, err := fs.Sub(assets.Migrations, "migrations/sqlite")
+	if err != nil {
+		t.Fatalf("migrations fs: %v", err)
+	}
+	if err := db.MigrateSQLite(path, migFS); err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+	database, err := db.OpenSQLite(path)
+	if err != nil {
+		t.Fatalf("open: %v", err)
+	}
+	defer database.Close()
+	assertComplete(t, NewSQLite(database))
+}
+
+func TestNewPostgres(t *testing.T) {
+	dsn := os.Getenv("TEST_DATABASE_URL")
+	if dsn == "" {
+		t.Skip("TEST_DATABASE_URL not set")
+	}
+	pool, err := pgxpool.New(context.Background(), dsn)
+	if err != nil {
+		t.Skipf("cannot connect: %v", err)
+	}
+	if err := pool.Ping(context.Background()); err != nil {
+		t.Skipf("cannot ping: %v", err)
+	}
+	t.Cleanup(pool.Close)
+	assertComplete(t, NewPostgres(pool))
+}