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/health_test.go

@@ -9,7 +9,6 @@ import (
 	"time"
 
 	"github.com/gin-gonic/gin"
-	"github.com/jackc/pgx/v5/pgxpool"
 
 	"shared-album/internal/config"
 	"shared-album/internal/storage"
@@ -24,23 +23,14 @@ func mustSigner(t *testing.T) *storage.Signer {
 	return signer
 }
 
-func lazyPool(t *testing.T) *pgxpool.Pool {
-	t.Helper()
-	pool, err := pgxpool.New(context.Background(), "postgres://u:p@127.0.0.1:1/x?sslmode=disable")
-	if err != nil {
-		t.Fatalf("pool: %v", err)
-	}
-	t.Cleanup(pool.Close)
-	return pool
-}
-
 func TestHealthStorageLabel(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	fs, err := storage.NewFS(t.TempDir(), mustSigner(t))
 	if err != nil {
 		t.Fatalf("fs: %v", err)
 	}
-	srv := &Server{cfg: &config.Config{}, pool: lazyPool(t), storage: fs}
+	ok := func(context.Context) error { return nil }
+	srv := &Server{cfg: &config.Config{}, ping: ok, storage: fs}
 
 	call := func() map[string]any {
 		rec := httptest.NewRecorder()