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

Makefile

@@ -1,4 +1,4 @@
-.PHONY: build frontend backend run migrate tidy test clean
+.PHONY: build frontend backend run migrate reconcile reconcile-delete tidy test clean
 
 frontend:
 	cd frontend && npm ci && npm run build
@@ -20,6 +20,15 @@ run: backend
 migrate:
 	cd backend && go run ./cmd/migrate
 
+# Reconcile object storage against the metadata journal (report only).
+reconcile:
+	cd backend && go run ./cmd/reconcile
+
+# Reconcile and delete orphaned blobs older than --min-age (default 1h).
+# Override the grace period when needed: make reconcile-delete MIN_AGE=1m
+reconcile-delete:
+	cd backend && go run ./cmd/reconcile --delete $(if $(MIN_AGE),--min-age $(MIN_AGE),)
+
 tidy:
 	cd backend && go mod tidy