feat: backend MVP (auth/rbac, catalog, orders, fulfillment, invoices) + specs + scaffolds

openspec/changes/fulfillment-invoices/proposal.md

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+# Proposal: fulfillment-invoices
+
+## Why
+After payment, merchants ship goods (发货单) and customers request invoices (发票). This phase closes the post-order loop of the MVP.
+
+## What changes
+- Schema: shipments (carrier, tracking, status, per-item qty), invoices (title, tax_no, kind, amount, status).
+- Shipment lifecycle: created(pending) → shipped → delivered; order becomes fulfilling on first shipment, shipped when all items shipped, completed when all delivered (customer confirm allowed).
+- Merchant APIs: create shipment for paid/fulfilling orders, mark shipped, list shipments/invoices, issue invoice.
+- Customer APIs: my shipments, confirm delivery, request invoice per order, my invoices.
+
+## Non-goals
+- Carrier API integrations, e-invoice/PDF generation, partial invoice amounts.
+
+## Capabilities
+- `shipment`: 发货单 lifecycle.
+- `invoice`: 发票 request/issue lifecycle.