fix: rename src/websocket to src/ws_manager to avoid websocket-client clash

selenium depends on websocket-client which installs a top-level
`websocket` package that shadows our src/websocket/ module on CI.
Renaming to ws_manager eliminates the conflict entirely — no more
sys.path hacks needed in conftest or Selenium tests.

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

tests/test_websocket.py

@@ -1,10 +1,10 @@
-"""Tests for websocket/handler.py — WebSocket manager."""
+"""Tests for ws_manager/handler.py — WebSocket manager."""
 
 import json
 
 import pytest
 
-from websocket.handler import WebSocketManager, WSEvent
+from ws_manager.handler import WebSocketManager, WSEvent
 
 
 def test_ws_event_to_json():