Adds the doc-mandated IiosIdempotencyCommand table + a reusable
IdempotencyService.run() that writes IN_FLIGHT at command start, replays the
cached response on a same-key/same-body retry, rejects a same-key/different-body
reuse (409), and retries a FAILED command. Tenant-scoped via
@@unique([scopeId, commandName, idempotencyKey]) (KG-02/KG-06).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
