Add cross-border NGN → USDC payment corridor

[MJ-RWA]

Complexity: High — 200 pts

Summary

One of Stellar's primary use cases is cross-border payments. This issue builds a "Send Money" flow targeting the NGN → USDC corridor — a key route for Nigerian users. It shows the live NGN/USD rate, calculates how much USDC the recipient gets, and executes everything in one Stellar path payment.

Files to Create/Modify

• Create: src/lib/forex.ts
• Create: src/pages/CorridorPage.tsx
• Modify: src/App.tsx — add /send-money route
• Modify: src/pages/DashboardPage.tsx — add "Send Money" quick action button

Implementation Notes

forex.ts

export async function getXlmNgnRate(): Promise<number | null>
export function calculateUsdcOutput(ngnAmount, xlmNgnRate, xlmUsdcRate): { xlmNeeded, usdcOut, effectiveRate }

Use CoinGecko's free /simple/price?ids=stellar&vs_currencies=ngn,usd endpoint (no key needed) for the NGN/XLM rate.

CorridorPage layout

You send (NGN equivalent): [50,000] NGN
≈ 28.5 XLM needed · Rate: 1 USD = 1,580 NGN
Recipient receives: ≈ $31.64 USDC
To: [G... address]   [Send Money]

• NGN input drives live calculation using getSwapQuote (XLM→USDC on-chain rate) multiplied by the live NGN/XLM rate
• Builds a single pathPaymentStrictSend operation (source XLM → destination USDC)
• Confirmation screen before signing shows: amount sent, amount received, exchange rate, network fee

Acceptance Criteria

• NGN input triggers live calculation of XLM and USDC amounts
• Uses CoinGecko or equivalent for live NGN/XLM rate (no API key required)
• Uses Horizon strictSendPaths for on-chain XLM/USDC rate
• Confirmation screen required before Freighter signing
• Single pathPaymentStrictSend transaction (not two separate ops)
• Success screen shows USDC received by recipient
• Works on Stellar mainnet

Screen Recording Requirements

1. Open Send Money, enter 50,000 NGN
2. Live FX rate loads — XLM needed and USDC output shown
3. Enter recipient Stellar address
4. Confirmation screen shows full breakdown
5. Sign with Freighter → payment executes in under 5 seconds
6. Recipient's USDC balance increased on Stellar Expert