Show live asset prices on dashboard via Lens

[Miracle656]

Summary

The dashboard shows balances but no fiat values. Pull live XLM and USDC prices from Lens (https://lens-ldtu.onrender.com) and display alongside.

Files

• frontend/wallet/app/dashboard/page.tsx
• new frontend/wallet/lib/lensClient.ts

Acceptance criteria

• Fetch /price/XLM:native/USDC:GBBD... on dashboard mount
• Show USD value next to each asset row
• Handle x402 payment flow if Lens requires it (or use free tier)
• Cache for ~30s to avoid spamming
• Skeleton loading while fetching