Add agent CLI, MCP server, and Codex plugin surface

[gaofeng21cn]

Summary

• Add a headless agent adapter and JSON CLI for validating config, running paper-title analyses, listing results, and reading result summaries.
• Add an optional MCP server plus project .mcp.json and a Codex plugin/skill surface for agent discovery.
• Return machine-readable run envelopes from the title pipeline while preserving the existing WebSocket all_done event.
• Document agent usage and repair tests for package imports / Python 3.14 event-loop behavior.

Validation

• python3 -m pytest -q test
• python3 -m compileall -q citationclaw test
• python3 /Users/gaofeng/.codex/skills/.system/skill-creator/scripts/quick_validate.py skills/citationclaw
• python3 - <<'PY'
  import citationclaw.mcp_server as server
  print('mcp_import=ok')
  PY
• CLI smoke with python3 -m citationclaw.agent_cli in test_mode: status=success, folder_count=1, record_count=5