feat(whiteboard) : add close button to whiteboard interface

[srijan2607]

This pull request adds a close button to the whiteboard feature, improving user experience by allowing users to easily close the whiteboard interface. The main changes include adding the button UI, styling it for accessibility and responsiveness, and connecting it to the application's state management.

Whiteboard close button feature:

• Added a close button (IconCloseLarge) to the whiteboard UI in Whiteboard.tsx, including keyboard accessibility (Enter/Space to close) and ARIA labeling for accessibility. [1] [2]
• Connected the close button to the Redux action toggleWhiteboard to properly update UI state when the button is used. [1] [2]

Styling and responsiveness:

• Introduced new CSS styles in _whiteboard.scss to position and style the close button, ensuring visibility, accessibility, and responsiveness (including adjustments for mobile browsers).

Before

Screen.Recording.2025-11-13.at.7.29.25.AM.mov

After

Screen.Recording.2025-11-13.at.7.32.28.AM.mov

[jitsi-jenkins]

Hi, thanks for your contribution!
If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.

[srijan2607]

@saghul @damencho Could you please take a look at the latest updates and approve the merge when convenient

[srijan2607]

@saghul can you take a look at this ??

[srijan2607]

Related issue #16678