feat(frontend): add stale price tooltip warning in FiatEquivalent when feed is older than 5 minutes

[aazminu]

Description

Exposes lastUpdatedAt from useTokenPrice (frontend/src/hooks/useTokenPrice.ts) and renders an amber info indicator with an accessible tooltip ("Price estimate last updated X minutes ago") in FiatEquivalent (frontend/src/components/FiatEquivalent.tsx) whenever the cached token price feed is older than 5 minutes (5 * 60 * 1000 ms).

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 #1640
Fixes #1640
/claim #1640

Changes Made

• Exposed lastUpdatedAt (number | null) on the object returned by useTokenPrice in frontend/src/hooks/useTokenPrice.ts (preferring query.data.timestamp with fallback to query.dataUpdatedAt).
• Added and exported getPriceStaleness(lastUpdatedAt, nowMs) and STALE_PRICE_THRESHOLD_MS (5 * 60 * 1000) in frontend/src/components/FiatEquivalent.tsx.
• Updated FiatEquivalent to render an amber info badge (data-testid="stale-price-warning", title, aria-label, and role="tooltip") reading "Price estimate last updated X minutes ago" when the price quote is older than 5 minutes.
• Guarded missing/null price data and timestamps so fresh quotes and loading/null states render cleanly without warnings or runtime errors.
• Added unit tests in frontend/src/components/__tests__/FiatEquivalent.test.tsx covering fresh quotes (< 5 minutes), stale quotes (> 5 minutes), and null/missing price data.

Testing

Test Coverage

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

Test Steps

1. Run npx vitest run src/components/__tests__/FiatEquivalent.test.tsx src/app/streams/[id]/__tests__/stream-details-content.test.tsx src/__tests__/a11y.test.tsx in frontend/ (29/29 tests pass).
2. Run npx tsc --noEmit in frontend/ (0 errors).
3. Run npx eslint src/hooks/useTokenPrice.ts src/components/FiatEquivalent.tsx src/components/__tests__/FiatEquivalent.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