Function theme 

pub fn theme() -> Theme

What: Access the application’s theme palette, loading or caching as needed.

Inputs:

• None.

Output:

• A copy of the currently loaded Theme.

Panics

• Panics if the theme store RwLock is poisoned

Details:

• Lazily initializes a global RwLock<Theme> using load_initial_theme.
• Subsequent calls reuse the cached theme until reload_theme updates it.