feat(frontend): add Today quick-jump disabled state and current-day highlight to CalendarView

[aazminu]

Description

Enhances CalendarView (frontend/src/components/dashboard/CalendarView.tsx) so the "Today" quick-jump button disables with subtle styling when already viewing the current month, and highlights the current calendar day cell with a distinct accent border ring (ring-2 ring-inset ring-accent), light/dark background tint, and a Today pill badge.

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 #1643
Fixes #1643
/claim #1643

Changes Made

• Computed isViewingCurrentMonth in frontend/src/components/dashboard/CalendarView.tsx to disable and subtly style the "Today" quick-jump button when already viewing the current system month/year, and highlight it with accent styling when browsing other months.
• Added accessible aria-label="Previous month" and aria-label="Next month" attributes to the calendar navigation arrows.
• Updated the current day cell (day.isToday) with data-testid="calendar-today-cell", aria-current="date", a distinct ring-2 ring-inset ring-accent border ring, light/dark mode contrast (bg-accent/10 dark:bg-accent/15), and a Today pill badge (data-testid="calendar-today-badge").
• Added unit tests in frontend/src/components/dashboard/CalendarView.test.tsx.

Testing

Test Coverage

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

Test Steps

1. Run npx vitest run src/components/dashboard/CalendarView.test.tsx in frontend/ (4/4 tests pass).
2. Run npx tsc --noEmit in frontend/ (0 errors).
3. Run npx eslint src/components/dashboard/CalendarView.tsx src/components/dashboard/CalendarView.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