Guard closed invoice payment events

[phucnguyen1707]

Summary

• only settle gig invoices from payable/open statuses when CoinPay reports confirmed or forwarded
• preserve rejected/cancelled invoices so stale payment events cannot revive them as paid
• apply the same closed-invoice guard to webhook metadata updates and payment-status sync

Tests

• ./node_modules/.bin/vitest run src/app/api/payments/coinpayportal/webhook/route.test.ts
• ./node_modules/.bin/vitest run src/lib/coinpay-payment-sync.test.ts
• ./node_modules/.bin/eslint src/app/api/payments/coinpayportal/webhook/route.ts src/app/api/payments/coinpayportal/webhook/route.test.ts src/lib/coinpay-payment-sync.ts src/lib/coinpay-payment-sync.test.ts
• ./node_modules/.bin/tsc --noEmit
• ./node_modules/.bin/vitest run --reporter=dot