feat: ingest HTTP 201/409 for event_id idempotency

- Validate UUID format; log created/duplicate/rejected

- Tests for 201, 409, 422; update agent-integration and work-plan

- Docs: neutral IDE wording (no product-specific editor names)

docs/INDEX.md

@@ -15,7 +15,7 @@
 | [ssl-certificate.md](ssl-certificate.md) | Wildcard TLS: формат, scp, пути `/etc/ssl/sac/` |
 | [deployment.md](deployment.md) | Эксплуатация, backup, TLS, `sac-deploy.sh` |
 | [operations-prod-status.md](operations-prod-status.md) | **Статус prod** и следующие шаги |
-| [workspace-three-repos.md](workspace-three-repos.md) | Cursor multi-root |
+| [workspace-three-repos.md](workspace-three-repos.md) | Multi-root workspace (три репо) |
 
 ## Порядок чтения