feat: Document Marketplace UI with SePay Checkout Flow

[ghost]

Opened by @roomote-v0 on behalf of Visser Lucas

Summary

Adds the frontend UI for the document marketplace with SePay bank transfer payment integration. Companion PR to vanchuongmandam/api-server#39.

Changes

Types & API Layer

• Added marketplace types: MarketDocument, Order, Purchase, UserProfile, BillingAddress
• Added API functions for documents, orders, purchases, and user profile management

New Pages

Route	Description
/documents	Document marketplace listing with search, category filter, sort, pagination
/documents/[slug]	Document detail with purchase/download buttons, stats, related articles
/documents/[slug]/checkout	Multi-step checkout: billing address -> order confirmation -> QR payment -> success
/profile	User profile editor with billing address management
/profile/purchases	User document library (purchased documents with download)
/profile/orders	Order history with status tracking and cancellation
/admin/documents	Admin document management (CRUD table)
/admin/orders	Admin order management with revenue stats and status filtering

Checkout Flow

1. User clicks "Buy" on document detail page
2. Billing address form (saved to profile for reuse)
3. Order confirmation with item summary
4. QR code payment page with bank transfer details
5. Auto-polling for payment confirmation (5s intervals)
6. Success page with download link

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View task on Roo Code Cloud

[ghost]

Rooviewer   See task

Found 3 issues to address before merging.

• PaginationControls prop mismatch (document-list-client.tsx): Component is called with { currentPage, totalPages, basePath } but expects { pagination, onPageChange, isLoading }, resulting in broken pagination on the documents listing page.
• Payment polling ignores order expiry (checkout/page.tsx): pollPayment only handles paid/confirmed but never reacts to expired/cancelled, leaving the user stuck on the payment spinner indefinitely after expiry.
• Unsafe document field cast in order link (profile/orders/page.tsx): order.items[0]?.document as string will produce [object Object] in the URL if the API returns a populated MarketDocument object.

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}

[ngtlowk]

okay