✨ Add macOS Help Book Integration

### Description

Add native macOS Help Book integration to CodeEdit.
Currently, CodeEdit does not provide built-in documentation or Help Viewer integration.
Adding a **Help Book (.help bundle)** would allow users to access offline help content via the system Help Viewer, just like Apple's own apps.

### Alternatives Considered

_No response_

### Additional Context

Modern macOS apps like Xcode and Finder still use Help Books for user documentation.
It also supports localization and indexing (hiutil) for search.

Would be great to integrate this in a future release.

### Screenshots

like this