Install bundled Rootcell skills for Cursor and Claude

[jimpudar]

Summary

• Add the bundled Rootcell skills to the Cursor CLI and Claude Code Home Manager modules so enabling either extension places the skills in the tool-specific global skill directory.
• Keep the existing Pi skill installation unchanged.
• Add regression coverage that checks both extension modules include the expected skill destinations and sources.

Testing

• Unit tests passed with bun run test:unit:vitest.
• Parsed both edited Nix modules successfully with nix-instantiate --parse.