feat: seller invoice actions - cancel, resend link, and detail management (#288)

[s6pa1rta3n-lab]

Summary

Resolves #288. Implements end-to-end seller invoice management actions:

• Invoice Cancellation: Sellers can cancel pending invoices directly from the invoice detail page and dashboard cards with a confirmation prompt and optimistic UI updates.
• Backend Authorization: Gated cancellation on POST /api/invoices/:id/cancel requiring the requesting wallet to match sellerPublicKey (returning 403 Forbidden on mismatch, 400 Bad Request if already paid/expired).
• Copy Actions: Direct Copy Pay Link and Copy Invoice ID buttons with toast feedback.
• Payment Proof Navigation: Jump to payment proof / view proof on paid invoices.
• Public Pay Page Handling: Dedicated CANCELLED status view on /pay/[id] preventing payment attempts.

Changes & Touch List (32 files changed, >= 25 from touch list)

Backend

• backend/src/routes/invoice.handlers.ts: Handled sellerPublicKey parameter in cancelInvoice with 403 on authorization failure and validation.
• backend/src/routes/invoice.routes.ts: Documented cancel endpoint seller authorization.
• backend/src/types/api.ts & backend/src/utils/validation.ts: Exported CancelInvoiceInput and cancelInvoiceSchema.
• backend/src/storage/invoice-storage.ts, backend/src/storage/memory-storage.ts, backend/src/storage/memory-invoice-storage.ts, backend/src/storage/postgres-invoice-storage.ts: Forwarded and enforced sellerPublicKey check and expiry check in storage layers.
• backend/src/services/invoice-memory.service.ts & backend/src/services/invoice.service.ts: Enforced seller wallet authorization in both memory and Postgres services.
• backend/tests/invoice-handlers.test.ts, backend/tests/invoice-service.test.ts, backend/tests/memory-storage.test.ts: Added unit tests covering cancellation authorization, 403 mismatch rejection, and status transitions.

Frontend

• frontend/app/invoice/[id]/page.tsx: Integrated connected wallet check, confirm prompt, and seller auth forwarding on cancel.
• frontend/app/dashboard/page.tsx: Added handleInvoiceCancelled optimistic handler and passed userWallet and onCancel to InvoiceCard.
• frontend/components/InvoiceCard.tsx: Added Cancel button for pending invoices (gated on seller wallet), Copy Pay Link, Copy ID with feedback, and jump to proof for paid invoices.
• frontend/app/pay/[id]/page.tsx: Added dedicated CANCELLED banner and message.
• frontend/components/PaymentButton.tsx: Added specific error message when attempting to pay a cancelled invoice.
• frontend/components/PaymentStatus.tsx: Added detailed CANCELLED status message.
• frontend/components/InvoiceForm.tsx & frontend/components/PaymentReceipt.tsx: Documented pending invoice lifecycle and proof generation.
• frontend/lib/api.ts: Updated cancel method signature to pass sellerPublicKey.
• frontend/lib/store.ts: Added isWalletSeller helper.
• frontend/lib/utils.ts: Enhanced getShareUrl to prefer window origin in client environment.
• frontend/lib/payment-page-state.js & frontend/lib/payment-page-state.d.ts: Added cancelled boolean property to pay page view state.
• frontend/lib/dashboard-history.js & frontend/lib/dashboard-history.d.ts: Added isInvoiceCancellable helper.
• frontend/tests/pay-page-status-matrix.test.js & frontend/tests/payment-page-state.test.js: Added assertions for matrix.CANCELLED.cancelled.
• frontend/tests/dashboard-history.test.js: Added unit tests asserting INVOICE_FILTERS and historicalInvoices handle CANCELLED status.
• README.md: Documented seller invoice management and cancellation under lifecycle.

Verification

• Backend: npm test (170/170 passing), npm run typecheck (0 errors)
• Frontend: npm test (203/203 passing), npm run test:a11y (31/31 passing), npm run typecheck (0 errors)

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC