Add interactive API docs at /docs endpoint

Swagger UI served via CDN for browsing OpenAPI spec.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -80,6 +80,7 @@ All detectors support: `AGGREGATOR_URL`, `CHECK_INTERVAL`, `THRESHOLD_WARNING`,
 | `/wake` | POST | Exit sleep mode |
 | `/status` | GET | Current state JSON |
 | `/events` | GET | List active events |
+| `/docs` | GET | Interactive API documentation (Swagger UI) |
 
 ### `/notify` Endpoint