[feature] Add trackpad gesture entries

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Discussed in #139

^{Originally posted by 7s4s6dq2rk-lgtm January 1, 2026}
Title:
Feature request: Allow manual or preset trackpad gesture entries (non-functional)

Body:
Hi, first of all thank you for KeyClu — I’m using it on macOS (Apple Silicon) mainly as a shortcut reference tool.

I understand that macOS trackpad gestures cannot be detected or handled like regular keyboard shortcuts due to system limitations.

However, I wanted to ask if you would consider one of the following lightweight improvements:

1. Allow users to manually add custom “gesture entries” as text-only references.
   Example:

   • Trackpad: Three-finger swipe up → Mission Control
   • Trackpad: Two-finger swipe left/right → Back / Forward

2. Alternatively, provide an optional preset list of default macOS trackpad gestures as a static reference section.

The goal is not to execute gestures, but simply to document and display them alongside keyboard shortcuts as part of a unified cheat sheet.

I believe this could add value without requiring gesture detection or deep system integration.

Thanks for your time and for maintaining KeyClu.