feat: add LP position transfer UI

[newmattock]

Fixes #27

Summary

• add a reusable Transfer Position modal with Stellar G-address validation, current-LP rejection, and the required payout warning
• add Transfer Position actions for funded LP portfolio rows and LP invoice-detail view
• call transfer_lp_position through a useTransaction wrapper and update local invoice funder state after success
• include current-main governance/federation fixes needed for build compatibility

Validation

• npm test -- src/components/tests/TransferPositionModal.test.tsx src/components/tests/LPPortfolioTransfer.test.tsx 'app/pay/[id]/tests/PayInvoice.test.tsx' --reporter verbose
• npm run lint -- src/components/TransferPositionModal.tsx src/components/LPPortfolio.tsx src/components/LPDashboard.tsx 'app/pay/[id]/page.tsx' src/hooks/useTransaction.ts src/utils/soroban.ts app/governance/page.tsx src/utils/federation.ts src/components/tests/TransferPositionModal.test.tsx src/components/tests/LPPortfolioTransfer.test.tsx 'app/pay/[id]/tests/PayInvoice.test.tsx'
• npm run build
• git diff --check
• local HTTP/browser smoke on http://localhost:3022/lp and http://localhost:3022/pay/1