Add store-item Excel export/import for bulk price and stock updates.

Dashboard can download grouped product variants and re-upload to update price and stock. Also expose Content-Disposition for downloads and keep related product/customer API docs in sync.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/website-api/AI_PROMPT.md

@@ -31,7 +31,7 @@ You are building a **Meshkee business website (storefront)**. You must use the M
 ### Typical bootstrap sequence
 1. `GET /tenants/{domain}` → branding + `businessId`
 2. Homepage: business-info, **static-images**, sliders, category-groups, brand-groups, store-specials
-3. Catalog: categories, products, store-items (`name` instant search: in-stock first, then `updatedAt`), **user-products** (customer stock listings)
+3. Catalog: categories, products (`GET /products/{slug}` includes `relatedProducts`: same category then same brand, in-stock first), store-items (`name` instant search: in-stock first, then `updatedAt`), **user-products** (customer stock listings)
 4. Auth: register/login → store tokens. Optional: `POST /auth/send-otp` then `POST /auth/login-otp` (passwordless) or `POST /auth/reset-password` (forgot password). `POST /auth/verify-otp` only marks the cell verified (no tokens).
 5. Cart checkout with `addressId` or inline `shippingAddress` + `payment`
    - For online pay: `payment.type = "e_payment_gate"`, `gatewayType` (e.g. `"mellat"` or `"zarinpal"`), and absolute `returnUrl`