Add /mcp interactive TUI toggle (arrow + space) like /skills option 2

Problem

/mcp shows MCP servers and their status, but there’s no quick in‑session interactive UI to enable/disable servers like /skills option 2.

Proposed behavior

• /mcp opens a TUI list of MCP servers with a checkbox per server.
• Arrow keys move selection; space toggles enable/disable.
• Visual status updates immediately.
• Optional: “Apply” and “Cancel” actions to confirm or revert.
• Optional: toggle session‑only vs persistent config (if supported).

Why this matters

Fast enable/disable is common when switching toolsets. A TUI flow consistent with /skills reduces friction and mistakes.

Acceptance criteria

• /mcp opens a selectable list (arrow keys to move, space to toggle).
• Toggling reflects immediate enable/disable status.
• State can be applied or discarded before exit.
• If persistence is supported, user can choose session‑only or saved change.

Related

• /mcp listing exists but is not interactive: #5161
• Broader MCP TUI RFC: #3778