feat: implement Stellar asset conversion and exchange rate ticker

[Fayyo]

Closes #64

Summary

Implements a real-time asset conversion and exchange rate ticker component for the dashboard, displaying live conversion rates between XLM, USDC, yUSDF, and AQUA on Stellar.

Changes

New files

• src/components/dashboard/AssetTicker.tsx — Responsive ticker component with skeleton loading, 24h change indicators, Lucide icons, and live badge. Polls every 30s via React Query.
• src/lib/stellar.ts — Stellar formatting utilities: formatStellarPrice (adaptive precision), formatAssetAmount, convertToUsd, and sortAssetRates (XLM-first ordering).
• src/services/mock/rates.ts — Mock rate data for XLM, USDC, yUSDF, and AQUA assets.

Modified files

• src/types/domain.ts — Added AssetRate interface.
• src/services/query-keys.ts — Added rates query key.
• src/services/resources.ts — Added getAssetRates resource function.
• src/services/mock/index.ts — Re-exports mock rates.
• src/hooks/use-queries.ts — Added useAssetRates hook with 30s refetch interval.

Acceptance Criteria

• ✅ Responsive layout with Lucide icons
• ✅ Rate formatting utilities with proper decimal places for Stellar assets
• ✅ React Query integration for fetching/caching with fallback mock data
• ✅ npm run typecheck — passes (no new errors; pre-existing errors in transactions/page.tsx are unrelated)
• ✅ npm run lint — passes (no new errors)
• ✅ Skeleton loading states prevent layout shift
• ✅ 24-hour percentage change indicators with directional arrows

Testing

• Validate responsiveness across mobile and desktop viewport sizes
• Verify no layout shift occurs during data loading states (skeleton screens match final layout)
• Confirm 24h change indicators display correctly (green ↑ positive, red ↓ negative, grey — neutral)

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[mergekeeper]

MergeKeeper review

Scope: in scope for linked issue #64.
Verdict: clean

The pull request correctly implements the Stellar asset conversion and exchange rate ticker component matching all requirements.

Reviewed commit: 497ba9102708f836fff6f04d2871b9a1f954bd78.
CI and merge eligibility are checked separately.

[mergekeeper]

MergeKeeper merge status

Status: blocked
PR state: open
Mergeability: unknown
Checked commit: 497ba9102708f836fff6f04d2871b9a1f954bd78.

Reason: One or more required CI checks failed.

Failing checks:

• build - view details

Next steps:

1. Open the failing check details above and fix the reported error.
2. Run the same checks locally where possible.
3. Commit and push the fix.
4. MergeKeeper will automatically re-review the updated PR.