feat(frontend): add aria-controls and Escape focus management to NotificationDropdown

[aazminu]

Description

Enhances NotificationDropdown (frontend/src/components/NotificationDropdown.tsx) with aria-controls linking the bell trigger button to the dropdown menu container (id="notifications-dropdown-menu"), accurate aria-expanded state exposure, aria-live="polite" unread announcement, and keyboard focus management that returns focus to the bell trigger button when dismissed via the Escape key or close button.

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🔧 Refactoring (no functional changes)
• ⚡ Performance improvement
• 🧪 Test addition or update

Related Issues

Closes #1636
Fixes #1636
/claim #1636

Changes Made

• Added triggerRef (useRef<HTMLButtonElement>(null)) and aria-controls="notifications-dropdown-menu" to the notification bell trigger button in frontend/src/components/NotificationDropdown.tsx.
• Added id="notifications-dropdown-menu" to the notification dropdown dialog container.
• Restored keyboard focus to triggerRef.current when Escape is pressed while the dropdown is open (or when the close button is activated).
• Added unit tests in frontend/src/components/NotificationDropdown.test.tsx verifying aria-expanded, aria-controls, aria-live announcement updates, and Escape key dismissal restoring focus to the bell trigger button.

Testing

Test Coverage

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed

Test Steps

1. Run npx vitest run src/components/NotificationDropdown.test.tsx in frontend/ (7/7 tests pass).
2. Run npx tsc --noEmit in frontend/ (0 errors).
3. Run npx eslint src/components/NotificationDropdown.tsx src/components/NotificationDropdown.test.tsx in frontend/ (0 errors, 0 warnings).

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have checked for breaking changes and documented them if applicable

Additional Notes

Payout Details

• USDT/USDC Receiving Wallet (EVM / ERC-20 / Polygon / Arbitrum / Optimism / Base / BSC): 0x9a51790aC01c54184bcFa067bC38f7F0E7C6F6B6