Add keyboard shortcuts for common operations

[FatBy]

Description

Add keyboard shortcuts for frequently used operations to improve power-user workflow.

Suggested Shortcuts

Shortcut	Action
Ctrl+K	Open/close AI chat panel
Ctrl+/	Focus chat input
Ctrl+Shift+S	Open settings
Escape	Close active panel/modal
Ctrl+1-5	Switch between sidebar tabs

Expected Behavior

• Consistent shortcut handling via a central keyboard event system
• A "Keyboard Shortcuts" help dialog (e.g., press ? to show)

Suggested Approach

1. Create a useKeyboardShortcuts hook
2. Register shortcuts at app root level
3. Add a help modal listing all shortcuts