ui: disable mcp extension shortcut when unfocused

[tiensi]

Summary Updated mcp extension shortcut to only toggle on when Goose window has focus

Testing

• Opened goose window
• ran ⌘⇧Y shortcut
• saw popup
• Navigated away from goose
• ran ⌘⇧Y shortcut
• no popup
• returned to goose window
• ran ⌘⇧Y shortcut
• saw popup

https://github.com/user-attachments/assets/8df732c3-e2f5-44e9-9f0f-249e7c0cb221

Issue @lily-de https://github.com/block/goose/issues/1347