feat(cad): launch Interactive CAD Agent & seaweed-safe FPV boat model.

[archat-hash]

🎯 Overview
This PR marks a significant evolution of FlyCLI's CAD capabilities, moving from simple script execution to a full
Interactive CAD Collaboration ecosystem. It introduces the Model Context Protocol (MCP) integration, allowing AI agents and
human designers to work together in real-time within FreeCAD. The centerpiece of this update is the co-designed
fpv_boat.stl.

✨ Key Changes

• Interactive CAD Engine: Updated assets/python/freecad_listener.py and launcher.cjs to support bidirectional state
  synchronization. The agent can now "inspect" human-made changes before proposing its own.
• FPV Boat Model: Inclusion of fpv_boat.stl, a seaweed-safe hull design developed through collaborative AI-human sessions.
• CAD Knowledge Base: Added docs/reference/cad-examples.md, providing the agent with robust code patterns for Part API and
  CadQuery.
• Human-in-the-Loop Protocol: Updated skills/flycli/SKILL.md with the "Synchronize-and-React" standard. This ensures the
  agent respects user intent and provides live feedback during the modeling process.

🛠 Technical Improvements

• Zero-File IPC: Modeling commands are now streamed directly to FreeCAD via IPC/STDIO, eliminating the need for temporary
  .py or .json files in the root directory.
• Process Persistence: Implemented detached process management to ensure the FreeCAD GUI remains open and interactive even
  if the CLI session restarts.
• Repository Hygiene: Updated .gitignore to exclude pycache and cleaned up legacy build artifacts.

🚢 How to Verify

1. Checkout to feature/fpv-boat.
2. Launch the CAD session: npx flycli cad.
3. Verify the model file: ls fpv_boat.stl.
4. Test the agent's awareness by asking it to "inspect the current document" after manually adding an object in FreeCAD.