API: Invoice CRUD Endpoints & PDF Generation

[0xdevcollins]

Summary

Implement full Invoice CRUD API endpoints and server-side PDF generation using Puppeteer.

Requirements

• POST /v1/invoices — Create invoice with line items, tax, discount, customer details
• GET /v1/invoices — List merchant invoices (paginated, filterable by status)
• GET /v1/invoices/:id — Get invoice detail
• PATCH /v1/invoices/:id — Update draft invoice
• DELETE /v1/invoices/:id — Cancel/delete draft invoice
• GET /v1/invoices/:id/pdf — Generate and return PDF
• PDF generation using Puppeteer rendering a React template
• Store PDFs in Cloudflare R2, save URL to pdfUrl field
• Multi-currency support (USD, EUR, NGN, etc.)
• Partial payment tracking
• Status lifecycle: DRAFT → SENT → VIEWED → PARTIALLY_PAID → PAID → OVERDUE → CANCELLED

Database

Invoice model already exists in Prisma schema. May need migration for additional fields.

Acceptance Criteria

• All CRUD endpoints functional with proper validation (Zod)
• PDF renders with merchant branding (logo, color)
• PDF stored in R2 and accessible via signed URL
• Partial payments update invoice status correctly
• Proper error handling with descriptive messages