Improve Keyboard Shortcuts tab UI and code structure

[Prashamtogadiya]

Description

This PR introduces a new "Keyboard Shortcuts" tab inside the Settings window.
It provides a complete overview of all available shortcuts and delivers the solution requested in #2037.

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Changes

• Added a new file: UITabKeyboardShortcuts.js containing the full list of keyboard shortcuts.
• Registered the new tab inside SettingsService.js so it appears in the Settings UI.
• Implemented structured categories for organizing shortcuts.

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Features

• Displays shortcuts grouped into clear categories:
  • General: Search, Undo, Close menus
  • Navigation: Arrow Keys, Enter, Tab
  • File Management: Copy, Paste, Cut, Delete
  • Windows: Close current window
• Styled key indicators for better clarity and readability.
• Responsive layout with proper Mac ⌘ command notation support.

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How to Access

Users can view the keyboard shortcuts by navigating to:

Settings → Keyboard Shortcuts

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Closes #2037

[CLAassistant]

All committers have signed the CLA.