feat(types): expose MCP server source in status

[fallintoplace]

What

• Add optional source to McpServerStatus.
• Document "sdk" while allowing other values.

Why

• Let callers see where each server came from.

Implementation

• Keep the CLI response unchanged and cover known and unrecognized sources.

[sigley]

Reviewed on exact head 8cc6e3961e7acf89914ec3583a97e8547220a4df.

This looks sound to me. Query.get_mcp_status() already returns the control response verbatim, so the runtime path does not need a parser change; the missing piece is the public TypedDict/documentation surface. Keeping source as an optional open str also avoids freezing the SDK to only the currently observed "sdk" value, and the tests cover both that known value and an unrecognized future value through the public status path.

I did not find a correctness issue in the change.