feat(inventory): 強化調撥單功能，支援販賣機貨道欄位、開放商品重複加入及優化過帳庫存檢核

app/Modules/Inventory/Services/TransferService.php

@@ -63,6 +63,7 @@ class TransferService
                     'product_id' => $data['product_id'],
                     'batch_number' => $data['batch_number'] ?? null,
                     'quantity' => $data['quantity'],
+                    'position' => $data['position'] ?? null,
                     'notes' => $data['notes'] ?? null,
                 ]);
                 // Eager load product for name
@@ -72,17 +73,20 @@ class TransferService
                 if ($oldItemsMap->has($key)) {
                     $oldItem = $oldItemsMap->get($key);
                     // 檢查數值是否有變動
-                    if ((float)$oldItem->quantity !== (float)$data['quantity'] || 
-                        $oldItem->notes !== ($data['notes'] ?? null)) {
+                    if ((float)$oldItem->quantity !== (float)$data['quantity'] ||
+                        $oldItem->notes !== ($data['notes'] ?? null) ||
+                        $oldItem->position !== ($data['position'] ?? null)) {
                         
                         $diff['updated'][] = [
                             'product_name' => $item->product->name,
                             'old' => [
                                 'quantity' => (float)$oldItem->quantity,
+                                'position' => $oldItem->position,
                                 'notes' => $oldItem->notes,
                             ],
                             'new' => [
                                 'quantity' => (float)$data['quantity'],
+                                'position' => $item->position,
                                 'notes' => $item->notes,
                             ]
                         ];
@@ -148,8 +152,10 @@ class TransferService
                     ->first();
 
                 if (!$sourceInventory || $sourceInventory->quantity < $item->quantity) {
+                    $availableQty = $sourceInventory->quantity ?? 0;
+                    $shortageQty = $item->quantity - $availableQty;
                     throw ValidationException::withMessages([
-                        'items' => ["商品 {$item->product->name} (批號: {$item->batch_number}) 在來源倉庫存不足"],
+                        'items' => ["商品 {$item->product->name} (批號: {$item->batch_number}) 在來源倉庫存不足。現有庫存：{$availableQty}，尚欠：{$shortageQty}。"],
                     ]);
                 }
 
@@ -182,6 +188,7 @@ class TransferService
                         'warehouse_id' => $order->to_warehouse_id,
                         'product_id' => $item->product_id,
                         'batch_number' => $item->batch_number,
+                        'location' => $item->position, // 同步貨道至庫存位置
                     ],
                     [
                         'quantity' => 0,