feat: add payer invoice search filters

[newmattock]

Fixes #18

Summary

• wire the payer invoice inbox into the shared URL-persisted invoice filter state
• add the shared InvoiceFilterBar above payer tabs with filtered tab counts and visible invoice totals
• upgrade token filtering from a single select to USDC/EURC/XLM multi-select checkboxes
• expand supported status filters to include payer lifecycle states like Disputed, Expired, and Appealed
• add focused coverage for invoice search, amount/status/date/discount filters, and multi-token filtering
• carry narrow current-main build fixes for governance status typing and related TypeScript compatibility issues

Validation

• npm test -- src/hooks/__tests__/useInvoiceFilters.test.ts --reporter verbose
• npm run lint -- app/payer/page.tsx src/components/InvoiceFilterBar.tsx src/hooks/useInvoiceFilters.ts src/hooks/__tests__/useInvoiceFilters.test.ts app/governance/page.tsx src/utils/federation.ts src/utils/evidence.ts src/components/TokenSelector.tsx
• npm run build
• git diff --check
• local smoke: curl -I http://localhost:3030/payer returned HTTP/1.1 200 OK