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/Procurement/Services/ProcurementService.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace App\Modules\Procurement\Services;
+
+use App\Modules\Procurement\Contracts\ProcurementServiceInterface;
+use App\Modules\Procurement\Models\PurchaseOrder;
+use Illuminate\Support\Collection;
+
+class ProcurementService implements ProcurementServiceInterface
+{
+    public function getPurchaseOrdersByDate(string $start, string $end, array $statuses = ['received', 'completed']): Collection
+    {
+        return PurchaseOrder::with(['vendor'])
+            ->whereIn('status', $statuses)
+            ->whereBetween('created_at', [$start . ' 00:00:00', $end . ' 23:59:59'])
+            ->get();
+    }
+
+    public function getPurchaseOrdersByIds(array $ids, array $with = []): Collection
+    {
+        return PurchaseOrder::whereIn('id', $ids)->with($with)->get();
+    }
+}