Feature request: toggle MCP directly in /mcp show list (Space key)

## Summary
Please add a direct toggle interaction in `/mcp show` so users can enable/disable a listed MCP server without typing its name.

## Current pain point
Today, users typically need commands like `/mcp disable ` or `/mcp enable `, which is slow when toggling frequently.

## Proposed behavior
- In `/mcp show`, display MCP servers as a selectable list with enabled/disabled state.
- Allow keyboard navigation (↑/↓).
- Press `Space` to toggle the selected MCP (on/off) immediately.
- Optional: `Enter` to confirm/save and `Esc` to cancel.

## Why this matters
- Faster MCP workflow with fewer keystrokes
- Better UX for users with multiple servers
- More discoverable and ergonomic than name-based commands