Stellar Asset (USDC) send/receive UX

[truthixify]

Tier: L (1-2 weeks) Type: feature

Context

Demo currently sends XLM only. USDC is the realistic use case. Add asset selector + trustline-aware flows on Send and Receive.

Scope

• Asset selector in StellarSend (XLM + USDC at minimum)
• Trustline detection: warn if recipient lacks trustline (link to fix)
• Use sdk's buildSendStellarAsset (from PR feat(storybook): add Storybook 8 with stories for Stellar components #32)
• Receive: display per-asset balances on stealth addresses
• Withdraw flow supports per-asset

Acceptance criteria

• Asset selector functional on Send
• Trustline detection working
• Per-asset balance display on Receive
• Per-asset withdraw
• Playwright test with USDC testnet

Files to start with

• src/components/StellarSend.tsx, StellarReceive.tsx