feat(inventory): 實作過期與瑕疵庫存總計顯示，並強化庫存明細過期提示

app/Modules/Inventory/Imports/ProductImport.php

@@ -63,8 +63,14 @@ class ProductImport implements ToModel, WithHeadingRow, WithValidation, WithMapp
             return null;
         }
 
+        // 處理商品代號：若為空則自動生成
+        $code = $row['商品代號'] ?? null;
+        if (empty($code)) {
+            $code = $this->generateRandomCode();
+        }
+
         return new Product([
-            'code' => $row['商品代號'],
+            'code' => $code,
             'barcode' => $row['條碼'],
             'name' => $row['商品名稱'],
             'category_id' => $categoryId,
@@ -81,10 +87,28 @@ class ProductImport implements ToModel, WithHeadingRow, WithValidation, WithMapp
         ]);
     }
 
+    /**
+     * 生成隨機 8 碼代號 (大寫英文+數字)
+     */
+    private function generateRandomCode(): string
+    {
+        $characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
+        $code = '';
+        
+        do {
+            $code = '';
+            for ($i = 0; $i < 8; $i++) {
+                $code .= $characters[rand(0, strlen($characters) - 1)];
+            }
+        } while (Product::where('code', $code)->exists());
+
+        return $code;
+    }
+
     public function rules(): array
     {
         return [
-            '商品代號' => ['required', 'string', 'min:2', 'max:8', 'unique:products,code'],
+            '商品代號' => ['nullable', 'string', 'min:2', 'max:8', 'unique:products,code'],
             '條碼' => ['required', 'string', 'unique:products,barcode'],
             '商品名稱' => ['required', 'string'],
             '類別名稱' => ['required', function($attribute, $value, $fail) {