Phase 9 / Task 9.2 (remainder): testcontainer'd gateway e2e for ahand DB+Redis scenarios

[winrey]

Context

PR <commit 4489eb8> shipped HTTP-level integration for the ahand gateway endpoints (controllers + guards + ValidationPipe + supertest, with the service layer mocked). That nails the wire contracts but explicitly skips the persistence + Redis layers.

This issue covers the remaining 5 scenarios from Phase 9 / Task 9.2 of the ahand integration plan (§ 9.4.4 / § 9.4.8 gateway integration matrix), which all need a testcontainer'd Postgres + Redis to exercise faithfully.

Scope

Add apps/server/apps/gateway/test/ahand-persistence.e2e-spec.ts plus a minimal Postgres + Redis fixture (testcontainers or shared pool — match existing wiki integration spec pattern at apps/server/apps/gateway/src/wikis/__tests__/integration/).

Cover:

1. Idempotent webhook: same eventId posted twice → first fires Redis presence + Socket.io emit, second returns 204 with no side effects.
2. Ownership enforcement: user A POSTs /devices/{B's id}/token/refresh → 404 (not 403; we don't reveal existence).
3. Concurrent register collision: 10 simultaneous POST /devices with the same hubDeviceId → exactly 1 succeeds, 9 get 409 (DB UNIQUE constraint on hub_device_id).
4. Redis outage: kill Redis mid-test → GET /devices still returns the row with isOnline: null, no 500.
5. Hub 5xx during register: stub mock-hub-admin to 500 on the first register call → DB transaction rolls back, no row visible on retry.

Acceptance criteria

• All 5 scenarios pass via pnpm --filter @team9/gateway test:e2e ahand-persistence
• Runtime < 60s in CI (dev tier acceptable)
• Fixtures co-located in test/fixtures/ and reusable from im-worker tests (Task 9.3)

References

• Phase 9 / Task 9.2 in docs/superpowers/plans/2026-04-22-ahand-integration-plan.md
• Existing HTTP-level integration: apps/server/apps/gateway/test/ahand-integration.e2e-spec.ts
• Existing wiki integration spec for testcontainer pattern: apps/server/apps/gateway/src/wikis/__tests__/integration/wiki-folder9.integration.spec.ts