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/config/config_test.go

@@ -12,15 +12,15 @@ func setRequiredEnv(t *testing.T) {
 }
 
 func TestLoadStorageBackend(t *testing.T) {
-	t.Run("defaults to s3", func(t *testing.T) {
+	t.Run("defaults to fs", func(t *testing.T) {
 		setRequiredEnv(t)
 		t.Setenv("STORAGE_BACKEND", "")
 		cfg, err := Load()
 		if err != nil {
 			t.Fatalf("load: %v", err)
 		}
-		if cfg.Storage.Backend != "s3" {
-			t.Fatalf("backend = %q, want s3", cfg.Storage.Backend)
+		if cfg.Storage.Backend != "fs" || cfg.Storage.FSRoot != "./data" {
+			t.Fatalf("storage = %+v", cfg.Storage)
 		}
 	})
 
@@ -37,13 +37,17 @@ func TestLoadStorageBackend(t *testing.T) {
 		}
 	})
 
-	t.Run("fs without root", func(t *testing.T) {
+	t.Run("fs empty root falls back to default", func(t *testing.T) {
 		setRequiredEnv(t)
 		t.Setenv("STORAGE_BACKEND", "fs")
 		t.Setenv("FS_ROOT", "")
 		t.Setenv("URL_SECRET", "")
-		if _, err := Load(); err == nil {
-			t.Fatal("expected error for fs without FS_ROOT")
+		cfg, err := Load()
+		if err != nil {
+			t.Fatalf("load: %v", err)
+		}
+		if cfg.Storage.FSRoot != "./data" {
+			t.Fatalf("FSRoot = %q, want ./data", cfg.Storage.FSRoot)
 		}
 	})
 
@@ -68,3 +72,63 @@ func TestLoadStorageBackend(t *testing.T) {
 		}
 	})
 }
+
+func TestLoadDatabaseBackend(t *testing.T) {
+	t.Run("defaults to sqlite", func(t *testing.T) {
+		setRequiredEnv(t)
+		t.Setenv("DB_BACKEND", "")
+		cfg, err := Load()
+		if err != nil {
+			t.Fatalf("load: %v", err)
+		}
+		if cfg.Database.Backend != "sqlite" || cfg.Database.SQLitePath != "./galo.db" {
+			t.Fatalf("database = %+v", cfg.Database)
+		}
+	})
+
+	t.Run("postgres requires password", func(t *testing.T) {
+		t.Setenv("JWT_SECRET", "s")
+		t.Setenv("PG_PASSWORD", "")
+		t.Setenv("DB_BACKEND", "postgres")
+		if _, err := Load(); err == nil {
+			t.Fatal("expected error for postgres without PG_PASSWORD")
+		}
+	})
+
+	t.Run("sqlite with path", func(t *testing.T) {
+		t.Setenv("JWT_SECRET", "s")
+		t.Setenv("PG_PASSWORD", "")
+		t.Setenv("DB_BACKEND", "sqlite")
+		t.Setenv("SQLITE_PATH", "/data/galo.db")
+		cfg, err := Load()
+		if err != nil {
+			t.Fatalf("load: %v", err)
+		}
+		if cfg.Database.Backend != "sqlite" || cfg.Database.SQLitePath != "/data/galo.db" {
+			t.Fatalf("database = %+v", cfg.Database)
+		}
+	})
+
+	t.Run("sqlite empty path falls back to default", func(t *testing.T) {
+		t.Setenv("JWT_SECRET", "s")
+		t.Setenv("PG_PASSWORD", "")
+		t.Setenv("DB_BACKEND", "sqlite")
+		t.Setenv("SQLITE_PATH", "")
+		cfg, err := Load()
+		if err != nil {
+			t.Fatalf("load: %v", err)
+		}
+		if cfg.Database.SQLitePath != "./galo.db" {
+			t.Fatalf("SQLitePath = %q, want ./galo.db", cfg.Database.SQLitePath)
+		}
+	})
+
+	t.Run("invalid backend", func(t *testing.T) {
+		t.Setenv("JWT_SECRET", "s")
+		t.Setenv("PG_PASSWORD", "p")
+		t.Setenv("DB_BACKEND", "mysql")
+		if _, err := Load(); err == nil {
+			t.Fatal("expected error for invalid backend")
+		}
+	})
+}