feat: 修正庫存與撥補單邏輯並整合文件

1. 修復倉庫統計數據加總與樣式。
2. 修正可用庫存計算邏輯（排除不可銷售倉庫）。
3. 撥補單商品列表加入批號與效期顯示。
4. 修正撥補單儲存邏輯以支援精確批號轉移。
5. 整合 FEATURES.md 至 README.md。

app/Modules/Finance/Models/UtilityFee.php

@@ -11,26 +11,25 @@ class UtilityFee extends Model
     use HasFactory;
 
     protected $fillable = [
-        'type', // 'electricity', 'water', 'gas', etc.
-        'billing_period_start',
-        'billing_period_end',
-        'due_date',
+        'transaction_date',
+        'category',
         'amount',
-        'usage_amount', // kWh, m3, etc.
-        'unit', // 度, 立方米
-        'status', // 'pending', 'paid', 'overdue'
-        'paid_at',
-        'payment_method',
-        'notes',
-        'receipt_image_path',
+        'invoice_number',
+        'description',
     ];
 
     protected $casts = [
-        'billing_period_start' => 'date',
-        'billing_period_end' => 'date',
-        'due_date' => 'date',
-        'paid_at' => 'datetime',
+        'transaction_date' => 'date',
         'amount' => 'decimal:2',
-        'usage_amount' => 'decimal:2',
     ];
+
+    public function tapActivity(\Spatie\Activitylog\Contracts\Activity $activity, string $eventName)
+    {
+        $activity->properties = $activity->properties->put('snapshot', [
+            'transaction_date' => $this->transaction_date->format('Y-m-d'),
+            'category' => $this->category,
+            'amount' => $this->amount,
+            'invoice_number' => $this->invoice_number,
+        ]);
+    }
 }