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>

kao.py

@@ -47,6 +47,8 @@ class KaoManager:
 
         # Build environment
         proc_env = os.environ.copy()
+        # Ensure the project root is on PYTHONPATH so detectors can import each other
+        proc_env["PYTHONPATH"] = str(self.base_dir) + os.pathsep + proc_env.get("PYTHONPATH", "")
         if env:
             proc_env.update(env)