feat(desktop): Add keyboard shortcuts to switch projects (Cmd+1, Cmd+2, etc.) #11837

Summary

Add keyboard shortcuts to quickly switch between open projects in the desktop app using Cmd+1 through Cmd+9 (or Ctrl+1-9 on Windows/Linux).

Use Case

When working with multiple projects open in the desktop app, users need a fast way to switch between them without using the mouse. This is a common UX pattern in:

• VS Code (Cmd+1-9 switches editor tabs)
• Chrome/Safari/Firefox (Cmd+1-9 switches browser tabs)
• Terminal apps like iTerm2

Proposed Implementation

1. Add a "Window" menu with numbered project entries (like browser tab lists)
2. Register global shortcuts Cmd+1 through Cmd+9 to switch to projects by their order in the project list
3. Show the shortcut hint next to each project in the menu

Technical Notes

The desktop package uses Tauri with @tauri-apps/api/menu for menu management. Shortcuts can be added via the accelerator property on MenuItem:

await MenuItem.new({
  text: "Project 1",
  accelerator: "CmdOrCtrl+1",
  action: () => switchToProject(0),
})

Acceptance Criteria

• Cmd+1 through Cmd+9 switch to projects 1-9 respectively
• Works on macOS (Cmd) and Windows/Linux (Ctrl)
• Projects are ordered by most recently opened or alphabetically (TBD)
• Menu shows current project with a checkmark
• Shortcuts are discoverable in a "Window" or "Projects" menu