feat: multi-agent SIP with Redis session lockout

- SessionService: Redis-backed session lock/unlock/refresh with 1hr TTL
- AgentConfigService: queries Agent entity, caches per-member config
- Auth login: resolves agent config, locks Redis session, returns SIP credentials
- Auth logout: unlocks Redis session, Ozonetel logout, clears cache
- Auth heartbeat: refreshes Redis TTL every 5 minutes
- Added ioredis dependency

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -31,6 +31,7 @@
     "@nestjs/websockets": "^11.1.17",
     "ai": "^6.0.116",
     "axios": "^1.13.6",
+    "ioredis": "^5.10.1",
     "reflect-metadata": "^0.2.2",
     "rxjs": "^7.8.1",
     "socket.io": "^4.8.3"