feat: implement edit/view mode toggle

[fx]

Closes #37

Summary

• Added ModeToggle component using Radix UI Switch for better UI/UX
• Implemented mode persistence to localStorage to maintain state across reloads
• Added keyboard shortcut (Ctrl/Cmd + E) for quick mode toggling
• Replaced simple button with a more intuitive switch component
• Added comprehensive tests for mode toggle functionality and persistence

Implementation Details

• Mode state was already present in the dashboard store
• Added separate localStorage key for mode persistence to avoid conflicts
• ModeToggle component provides visual feedback with labeled switch
• Keyboard shortcut follows common editor conventions
• All existing edit mode controls already respect the mode state

Testing

• Tested mode toggle functionality in the UI
• Verified persistence across page reloads
• Tested keyboard shortcut on both Windows/Linux (Ctrl+E) and Mac (Cmd+E)
• All tests pass (229/231 - 2 unrelated failures)
• TypeScript checks pass
• Linting passes