feat: build invoice dispute UI

[newmattock]

Fixes #16

Summary

• add a payer-only Raise Dispute action for funded invoices on the invoice settlement page
• add a dispute modal with evidence text validation and the required governance-sharing warning
• hash evidence client-side with SHA-256 and pass the hash to dispute_invoice through useTransaction
• update local invoice status to Disputed after a successful dispute transaction
• include focused tests for hashing, modal validation, payer gating, and transaction wiring
• include current-main governance/federation build fixes

Validation

• npm test -- src/utils/tests/disputeEvidence.test.ts src/components/tests/DisputeInvoiceModal.test.tsx 'app/pay/[id]/tests/PayInvoice.test.tsx' --reporter verbose\n- npm run lint -- src/utils/disputeEvidence.ts src/components/DisputeInvoiceModal.tsx src/hooks/useTransaction.ts 'app/pay/[id]/page.tsx' 'app/pay/[id]/tests/PayInvoice.test.tsx' src/utils/tests/disputeEvidence.test.ts src/components/tests/DisputeInvoiceModal.test.tsx src/utils/soroban.ts app/governance/page.tsx src/utils/federation.ts\n- npm run build\n- git diff --check\n- local HTTP smoke: HEAD /pay/1 returned 200 on port 3024\n- in-app browser smoke found the pay route shell and invoice-not-found fallback on /pay/1 when RPC had no invoice Implement Stellar wallet connection with Freighter support  #1