Bump to v2.3.0: replace polling with SSE stream, fix detector imports

- Add GET /stream SSE endpoint to aggregator.py; state is pushed
  instantly on every change instead of fetched every 2s
- Replace setInterval polling in index.html with EventSource;
  onerror shows the ( ?.?) face and auto-reconnect is handled by
  the browser natively
- Fix ModuleNotFoundError in detectors: inject project root into
  PYTHONPATH when launching subprocesses from kao.py
- Update openapi.yaml, CLAUDE.md, README.md with /stream endpoint
- Remove completed SSE item from TODO.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -87,7 +87,8 @@ All detectors support: `AGGREGATOR_URL`, `CHECK_INTERVAL`, `THRESHOLD_WARNING`,
 | `/notify` | POST | Notification with optional customization (see below) |
 | `/sleep` | POST | Enter sleep mode |
 | `/wake` | POST | Exit sleep mode |
-| `/status` | GET | Current state JSON |
+| `/stream` | GET | SSE stream — pushes state JSON on every change (used by the frontend) |
+| `/status` | GET | Current state JSON (one-shot query) |
 | `/events` | GET | List active events |
 | `/docs` | GET | Interactive API documentation (Swagger UI) |