- Create apps/api/src/routes/push.ts: GET /vapid-public-key, POST /subscription (upsert), DELETE /subscription (user-scoped)
- Wire pushRouter at /api/push in index.ts
- Call webpush.setVapidDetails() in isMainModule() guard before serve()
- Fix broken vi.getMockImplementation scaffold bug in push.test.ts (Rule 1)
- push.test.ts: all 4 tests GREEN
