feat: customizable activation shortcut and settings UI

[YuniorGlez]

This PR introduces the ability to customize the activation keyboard shortcut for the Agentation toolbar, addressing the conflict with Chrome's Tab Search shortcut (#44).

Key changes:

• Added 'activationShortcut' prop to Agentation component (default: 'mod+Shift+A').
• New 'Shortcut Recorder' in the Settings panel allows users to visually define their own shortcut at runtime.
• Shortcuts are persisted in localStorage.
• Uses 'mod' keyword for automatic cross-platform mapping (Cmd on Mac, Ctrl on others).
• Updated UI feedback: the collapsed toolbar tooltip now shows the current shortcut.
• Updated documentation and example application.

Closes #44

[vercel]

@YuniorGlez is attempting to deploy a commit to the Benji Taylor's Projects Team on Vercel.

A member of the Team first needs to authorize it.