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/albums/repository.go

@@ -0,0 +1,18 @@
+package albums
+
+import (
+	"context"
+
+	"shared-album/internal/models"
+)
+
+// Repository is the persistence contract for the albums domain.
+type Repository interface {
+	Create(ctx context.Context, a *models.Album) error
+	OwnerID(ctx context.Context, id string) (string, error)
+	GetByID(ctx context.Context, id string) (*models.Album, error)
+	ListForUser(ctx context.Context, userID string) ([]models.Album, error)
+	Update(ctx context.Context, a *models.Album) error
+	Delete(ctx context.Context, id string) error
+	TrashPhotosByAlbum(ctx context.Context, albumID string) error
+}

backend/internal/albums/service.go

@@ -18,13 +18,13 @@ type MemberLookup interface {
 }
 
 type Service struct {
-	store   *Store
+	store   Repository
 	members MemberLookup
 	hub     *sse.Hub
 	storage storage.Backend
 }
 
-func NewService(store *Store, members MemberLookup, hub *sse.Hub, storage storage.Backend) *Service {
+func NewService(store Repository, members MemberLookup, hub *sse.Hub, storage storage.Backend) *Service {
 	return &Service{store: store, members: members, hub: hub, storage: storage}
 }
 

backend/internal/albums/sqlite_store.go

@@ -0,0 +1,142 @@
+package albums
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"time"
+
+	"shared-album/internal/models"
+	"shared-album/internal/sqliteutil"
+)
+
+// SQLiteStore is the SQLite implementation of Repository.
+type SQLiteStore struct {
+	db *sql.DB
+}
+
+func NewSQLiteStore(db *sql.DB) *SQLiteStore { return &SQLiteStore{db: db} }
+
+func (s *SQLiteStore) Create(ctx context.Context, a *models.Album) error {
+	var createdAt, updatedAt string
+	err := s.db.QueryRowContext(ctx,
+		`INSERT INTO albums (id, owner_id, title, description, cover_photo_id)
+		 VALUES ($1, $2, $3, $4, $5)
+		 RETURNING created_at, updated_at`,
+		a.ID, a.OwnerID, a.Title, a.Description, a.CoverPhotoID,
+	).Scan(&createdAt, &updatedAt)
+	if err != nil {
+		return err
+	}
+	a.CreatedAt = sqliteutil.ParseTime(createdAt)
+	a.UpdatedAt = sqliteutil.ParseTime(updatedAt)
+	return nil
+}
+
+func (s *SQLiteStore) OwnerID(ctx context.Context, id string) (string, error) {
+	var ownerID string
+	err := s.db.QueryRowContext(ctx, `SELECT owner_id FROM albums WHERE id = $1`, id).Scan(&ownerID)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			return "", ErrNotFound
+		}
+		return "", err
+	}
+	return ownerID, nil
+}
+
+const sqliteAlbumColumns = `a.id, a.owner_id, a.title, a.description, a.cover_photo_id,
+	a.created_at, a.updated_at, COALESCE(co.storage_key, ''),
+	(SELECT count(*) FROM photos WHERE album_id = a.id),
+	(SELECT count(*) FROM album_members WHERE album_id = a.id)`
+
+const sqliteAlbumJoins = `
+	LEFT JOIN photo_objects cpo ON cpo.photo_id = a.cover_photo_id AND cpo.role = 'thumb'
+	LEFT JOIN objects co ON co.id = cpo.object_id`
+
+func scanSQLiteAlbum(scan func(...any) error) (*models.Album, error) {
+	var a models.Album
+	var cover sql.NullString
+	var createdAt, updatedAt string
+	if err := scan(&a.ID, &a.OwnerID, &a.Title, &a.Description, &cover, &createdAt, &updatedAt,
+		&a.CoverThumbKey, &a.PhotosCount, &a.MembersCount); err != nil {
+		return nil, err
+	}
+	if cover.Valid {
+		a.CoverPhotoID = &cover.String
+	}
+	a.CreatedAt = sqliteutil.ParseTime(createdAt)
+	a.UpdatedAt = sqliteutil.ParseTime(updatedAt)
+	return &a, nil
+}
+
+func (s *SQLiteStore) GetByID(ctx context.Context, id string) (*models.Album, error) {
+	row := s.db.QueryRowContext(ctx,
+		`SELECT `+sqliteAlbumColumns+` FROM albums a`+sqliteAlbumJoins+` WHERE a.id = $1`, id)
+	a, err := scanSQLiteAlbum(row.Scan)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			return nil, ErrNotFound
+		}
+		return nil, err
+	}
+	return a, nil
+}
+
+func (s *SQLiteStore) ListForUser(ctx context.Context, userID string) ([]models.Album, error) {
+	rows, err := s.db.QueryContext(ctx,
+		`SELECT `+sqliteAlbumColumns+` FROM albums a
+		 LEFT JOIN album_members m ON m.album_id = a.id AND m.user_id = $1`+sqliteAlbumJoins+`
+		 WHERE a.owner_id = $1 OR m.user_id IS NOT NULL
+		 ORDER BY a.created_at DESC`, userID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []models.Album{}
+	for rows.Next() {
+		a, err := scanSQLiteAlbum(rows.Scan)
+		if err != nil {
+			return nil, err
+		}
+		out = append(out, *a)
+	}
+	return out, rows.Err()
+}
+
+func (s *SQLiteStore) Update(ctx context.Context, a *models.Album) error {
+	var updatedAt string
+	err := s.db.QueryRowContext(ctx,
+		`UPDATE albums
+		 SET title = $2, description = $3, cover_photo_id = $4, updated_at = $5
+		 WHERE id = $1
+		 RETURNING updated_at`,
+		a.ID, a.Title, a.Description, a.CoverPhotoID, sqliteutil.FormatTime(time.Now().UTC()),
+	).Scan(&updatedAt)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			return ErrNotFound
+		}
+		return err
+	}
+	a.UpdatedAt = sqliteutil.ParseTime(updatedAt)
+	return nil
+}
+
+func (s *SQLiteStore) Delete(ctx context.Context, id string) error {
+	res, err := s.db.ExecContext(ctx, `DELETE FROM albums WHERE id = $1`, id)
+	if err != nil {
+		return err
+	}
+	if n, _ := res.RowsAffected(); n == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
+func (s *SQLiteStore) TrashPhotosByAlbum(ctx context.Context, albumID string) error {
+	_, err := s.db.ExecContext(ctx,
+		`UPDATE photos SET deleted_at = $2 WHERE album_id = $1 AND deleted_at IS NULL`,
+		albumID, sqliteutil.FormatTime(time.Now().UTC()))
+	return err
+}