feat: add QQ quiet mode

[Suncloyum]

Summary

• add QQ_QUIET_MODE to suppress routine progress updates in QQ chats
• keep final answers, errors, files, images, and human-assistance prompts visible
• add a small quiet-mode filtering test and document the env var

Closes #21

Testing

• uv run python test_agent_runner_quiet_mode.py
• python -m compileall config.py _agent_runner.py test_agent_runner_quiet_mode.py
• git diff --check