feat(ui): improve keyboard accessibility for widgets and toolbar

[DhyaniKavya]

issue: #5809

Problem:-
Several interactive UI elements in Music Blocks are not accessible via keyboard navigation.

-Toolbar icons use elements without href, making them non-focusable and unreachable using the Tab key
-Widget buttons are created using

elements with only onclick handlers
-These elements lack role="button" and tabindex="0"
-Keyboard users cannot activate controls using Enter or Space
-Screen readers cannot correctly identify these elements as interactive controls
-This results in violation of WCAG 2.1 (2.1.1 Keyboard, 4.1.2 Name, Role, Value)

While the UI functions correctly with a mouse, it is not accessible to keyboard-only users or assistive technologies.

Solution:-
This PR improves keyboard accessibility while preserving all existing functionality:

-adds role="button" to non-semantic interactive elements
-adds tabindex="0" to enable keyboard focus
-adds keydown handlers to trigger click events on Enter and Space
-does not alter existing click behavior
-does not modify layout or styling

Changes Made:-

-File modified:
-> js/widgets/widgetWindows.js
-> add role="button" to dynamically created widget buttons
-> add tabindex="0" to widget buttons
-> add keydown handler for Enter/Space activation

-File modified:
-> index.html
-> add role="button" to toolbar anchor elements
-> add tabindex="0" to toolbar icons

Testing Performed:-

-Manual Verification
-Toolbar icons reachable via Tab
-Widget buttons focusable using keyboard
-Enter activates controls
-Space activates controls
-Focus order remains logical
-No console errors observed

-Automated Testing

Jest: ✅ all tests passed
Prettier: ✅ formatting verified
ESLint: ⚠️ pre-existing repository configuration warning (no new lint errors introduced)

Impact:-

-Improves keyboard accessibility across the application
-Enables inclusive access for keyboard-only users
-Improves screen reader compatibility
-Enhances WCAG 2.1 compliance
-No breaking changes

Notes:-
This change is intentionally minimal and non-breaking. It enhances accessibility without modifying core logic, UI behavior, or styling. The implementation follows standard accessibility best practices and preserves all existing interactions.

Happy to adjust if maintainers prefer a different approach.

[github-actions]

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

[DhyaniKavya]

@walterbender @omsuneri Please review these changes if they are useful and if any changes are required i am open to address them . Thankyou