Add category SEO description for storefront category pages.

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

prisma/migrations/20260927193000_category_seo_description/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "Category" ADD COLUMN IF NOT EXISTS "seoDescription" TEXT NOT NULL DEFAULT '';

prisma/schema.prisma

@@ -151,6 +151,8 @@ model Category {
   packages         String[]   @default([])
   /// Ordered form-builder defs: [{ id, labelFa, labelEn?, type: "text", required? }]
   technicalFields  Json       @default("[]")
+  /// Long-form SEO / category page copy shown on the storefront
+  seoDescription   String     @default("")
   products         Product[]
 
   @@index([storeId])