fix: Make Toolbar and Menu Buttons Keyboard Accessible

[Rahul-R79]

Related Issue:
Fixes #5113

Description:
This Pull Request addresses a significant accessibility barrier in the Music Blocks application. Many interactive elements in the main toolbar, auxiliary toolbar, and dropdown menus were implemented using <a> tags without href attributes. This prevented keyboard users from focusing on or activating these elements.

Changes:

• Added role="button" to all identified <a> tags that function as buttons.
• Added tabindex="0" to these same tags to make them focusable via the keyboard sequence.
• Formatted index.html using Prettier for consistent code style.

Affected Areas:

• Main Toolbar: Play, Stop, Record, FullScreen, New, Load, Save, etc.
• Auxiliary Toolbar: Speed controls, Plugin controls, Scroll toggles, etc.
• Dropdown Menus: Save options, Language options, Theme options.

How to Test:

1. Open the application.
2. Do not use the mouse.
3. Press the Tab key repeatedly to navigate through the toolbar items.
4. Verify that each icon receives visual focus.
5. (Optional) Use a screen reader to verify that the elements are announced as "buttons".

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[Rahul-R79]

Hi @omsuneri @walterbender

Could you please review these accessibility improvements? I've made the toolbar and menu icons keyboard-accessible by adding role="button" and tabindex="0". This ensures users can navigate the main interface using just the keyboard.

Thanks!