feat: build invoice submission form route

[newmattock]

Fixes #11

Summary

• Add /invoices/new as the freelancer invoice submission route.
• Redirect successful submissions to /invoices/[id] through a form onSubmitted callback.
• Add the optional referral code field requested by the issue while keeping it out of the current contract call.
• Add payer/self validation so freelancers cannot submit invoices to their own connected wallet address.
• Carry narrow current-main build fixes for governance status typing, token selector helper types, and federation account typing.

Validation

• npm test -- src/components/__tests__/SubmitInvoiceForm.test.tsx app/invoices/new/__tests__/NewInvoicePage.test.tsx --pool forks --maxWorkers 1 --reporter verbose
• npm run lint -- app/invoices/new/page.tsx app/invoices/new/__tests__/NewInvoicePage.test.tsx src/components/SubmitInvoiceForm.tsx src/components/__tests__/SubmitInvoiceForm.test.tsx src/utils/invoiceSubmission.ts app/governance/page.tsx src/components/TokenSelector.tsx src/utils/federation.ts
• git diff --check
• npm run build
• curl -I http://127.0.0.1:3033/invoices/new