feat(admin): implement variant management — list, create, edit, preview, activate/deactivate, delete (Plan 05)

- Extend addVariant with dimension fields and SKU uniqueness check; expand updateVariant to full field set; update getByIdForAdmin to return all variants (active + inactive)
- Add generateSku utility to @repo/utils; auto-generates SKU from brand, product name, attributes, and weight with manual-override support
- Move ProductSearchSection to components/shared and fix nav link /variants → /variant
- Variants page: product search, loading skeleton, variants table, toolbar with create button
- VariantsTable: 8 columns, activate/deactivate toggle, delete with AlertDialog confirmation
- VariantPreviewDialog: read-only full variant details with sections for pricing, inventory, shipping, attributes
- VariantForm: zod schema with superRefine for dimension and on-sale validation, auto-SKU generation
- CreateVariantDialog and EditVariantDialog wiring dollarsToCents on submit
- Install sonner and add Toaster to root layout; install ShadCN Switch component

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/utils/src/index.ts

@@ -166,6 +166,44 @@ export function getTotalPages(total: number, limit: number): number {
   return Math.ceil(total / limit);
 }
 
+// ─── SKU Generation ───────────────────────────────────────────────────────────
+
+/**
+ * Generate a SKU from product metadata.
+ * e.g. Royal Canin, Adult Dog Food, flavor: Chicken, 5kg → "ROY-CANI-ADUL-DOG-CHIC-5KG"
+ */
+export function generateSku(
+  brand: string,
+  productName: string,
+  attributes?: {
+    size?: string;
+    flavor?: string;
+    color?: string;
+  },
+  weight?: number,
+  weightUnit?: string
+): string {
+  const clean = (str: string) =>
+    str
+      .toUpperCase()
+      .trim()
+      .replace(/[^A-Z0-9\s]/g, "")
+      .split(/\s+/)
+      .map((w) => w.slice(0, 4))
+      .join("-");
+
+  const parts = [
+    brand       ? clean(brand)       : null,
+    productName ? clean(productName) : null,
+    attributes?.flavor ? clean(attributes.flavor) : null,
+    attributes?.size   ? clean(attributes.size)   : null,
+    attributes?.color  ? clean(attributes.color)  : null,
+    weight && weightUnit ? `${weight}${weightUnit.toUpperCase()}` : null,
+  ].filter(Boolean);
+
+  return parts.join("-");
+}
+
 // ─── Misc ─────────────────────────────────────────────────────────────────────
 
 /**