Price catalogue backup and restore

The price catalogue is PostgreSQL data (server/catalog/README.md). The SQLite catalog.db, its scheduled .db backups, pre-migration snapshots, leases and the catalog-backup restore CLI are gone with the file they protected.

• Restore: use the database's point-in-time restore (Replit PostgreSQL). Catalogue writes are transactional and append-only for prices, so a restore to a moment before a bad edit or import is exact.
• Manual copy: npm run catalog:export -- --out catalogue.json (or GET /api/price-catalog/export) writes every catalogue table, read in one transaction, as one JSON document (mode 0600) to keep, diff or hand over.
• Undoing a price change needs no restore: prices are append-only item_prices rows (GET /api/price-catalog/items/<code>/prices); set the old price again and a new row records it, with history.
• Moving a SQLite catalogue in (cutover, or an old backup .db): npm run catalog:import-legacy -- <catalog.db> --dry-run, then without --dry-run. It is verified and all-or-nothing.

The CLIs read and write the database DATABASE_URL (or FIELD_DB_URL) names. In a Replit workspace shell that is the workspace's own database, not production's (docs/REPLIT.md "Database"). For a copy of production's catalogue, use GET /api/price-catalog/export on the published app.