feat(procurement): 統一採購單按鈕樣式與術語更名為「作廢」，並加強權限控管

app/Modules/Procurement/Models/PurchaseOrder.php

@@ -70,4 +70,50 @@ class PurchaseOrder extends Model
     {
         return $this->hasMany(PurchaseOrderItem::class);
     }
+
+    /**
+     * 檢查是否可以轉移至新狀態，並驗證權限。
+     */
+    public function canTransitionTo(string $newStatus, $user = null): bool
+    {
+        $user = $user ?? auth()->user();
+        if (!$user) return false;
+        if ($user->hasRole('super-admin')) return true;
+
+        $currentStatus = $this->status;
+
+        // 定義合法的狀態轉移路徑與所需權限
+        $transitions = [
+            'draft' => [
+                'pending' => 'purchase_orders.view', // 基本檢視者即可送審
+                'cancelled' => 'purchase_orders.cancel',
+            ],
+            'pending' => [
+                'approved' => 'purchase_orders.approve',
+                'draft' => 'purchase_orders.approve', // 退回草稿
+                'cancelled' => 'purchase_orders.cancel',
+            ],
+            'approved' => [
+                'cancelled' => 'purchase_orders.cancel',
+                'partial' => null, // 系統自動轉移，不需手動權限點
+            ],
+            'partial' => [
+                'completed' => null, // 系統自動轉移
+                'closed' => 'purchase_orders.approve', // 手動結案通常需要核准權限
+                'cancelled' => 'purchase_orders.cancel',
+            ],
+        ];
+
+        if (!isset($transitions[$currentStatus])) {
+            return false;
+        }
+
+        if (!array_key_exists($newStatus, $transitions[$currentStatus])) {
+            return false;
+        }
+
+        $requiredPermission = $transitions[$currentStatus][$newStatus];
+        
+        return $requiredPermission ? $user->can($requiredPermission) : true;
+    }
 }