POC: add `mcp` command

[vito]

Usage: add dagger mcp as an MCP server.

Defaults to stdio. For SSE (handy for debugging), set PORT=1234 and configure http://localhost:1234/sse.

TODO:

• [ ] Should it be scoped per-chat somehow? Haven't found an easy way to do this with Claude Desktop. It literally runs a single MCP server for the entire time Desktop is open.
  • Goose does one-MCP-server-per-chat which feels much more reasonable. Maybe don't care about Claude Desktop.
• [ ] Some more prompt engineering for shell
• [ ] Shell commands are currently trying to run e.g. wolfi instead of github.com/dagger/dagger/modules/wolfi.
  • Arguably this feels like a correct assumption on the part of the LLM. Why do top-level Query fields not translate to toplevel commands? 🤔