Add six v7 WsFrameType enum members (index_session_start/cancel/batch,
index_file_result/progress/done), wire dispatch in device_ws message loop,
and implement _handle_index_session_start/cancel/file_batch with per-file
summarisation, token accounting, and quota enforcement.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
