Add TUI console toggler for MCP servers

[alecuba16]

Thanks for implementing the MCP default config handling. It would be better with a TUI console toggler as follow-up, so users can enable/disable configured MCP servers from the console without editing config or restarting.

Reference branch: https://github.com/alecuba16/jcode/tree/feature/mcp-server-toggles

Squashed commit: 6da79c04

Compare: master...alecuba16:jcode:feature/mcp-server-toggles

That branch adds the /mcp picker / Space toggle flow and keeps disabled MCP tools out of prompts at runtime.

[1jehuang]

Triage: reasonable follow-up to the MCP default-config work. An /mcp picker with Space-to-toggle, plus keeping disabled server tools out of prompts at runtime, fits the existing inline picker patterns. Marked needs-decision for maintainer review of the UX (persistence semantics: per-session vs written back to config, and interaction with already-connected servers). Reference branch noted (alecuba16:feature/mcp-server-toggles, 6da79c0).