fix: bound websocket queue overrides

[Justinabox]

Summary

• validate callstack_ws_queue_size as a non-boolean positive integer before the WebSocket upgrade, subscription, or queue construction
• preserve the default bounded queue size of 32 and honor valid positive overrides
• add resolver, invalid-override endpoint, and endpoint queue-construction regression coverage

Closes #286

Verification

• git diff --check
• PYTHONPATH=. uv run --no-project --with pytest --with pytest-asyncio --with pytest-aiohttp --with pyserial-asyncio --with aiosqlite pytest tests/test_websocket.py -q → 36 passed
• PYTHONPATH=. uv run --no-project --with pytest --with pytest-asyncio --with pytest-aiohttp --with pyserial-asyncio --with aiosqlite pytest tests/ -q → 1120 passed

Risks

Invalid in-process app overrides now fail before a WebSocket connection is prepared; the existing application has no public configuration surface for this internal override. Valid overrides retain the existing drop-oldest, PII-safe overflow behavior.