Fix creation responses without storage metadata

[pallaoro]

Creating a customer, product or invoice through the metadata-less STORAGE binding saved the row but returned HTTP 500; adding an invoice line saved it but returned 404. Callers could retry a successful write or fail to navigate to the new record.

Read each generated ID with INSERT … RETURNING id, following the existing journal creation pattern. Keep the line lookup after totals recomputation so the response contains the calculated amounts. No schema or dependency changes.

Validation: six new HTTP regressions fail on the base commit; all 62 tests and the Vite build pass with the fix. Coverage includes concurrent creates returning their own persisted rows, the complete customer/product/draft/line/issue flow, and a locked-period refusal leaving state unchanged. Independent review also passed the create/issue/concurrent-create/locked-period flows in workerd with both a SQLite Durable Object service binding returning only {rows} and D1. No production deployment was performed.