feat: 實作後台導航選單系統與狀態持久化

- 新增 14 個模組的路由與控制器佔位符
- 實作可展開式側邊欄選單 (Sidebar Menu)
- 優化選單樣式與主題適配
- 實作選單展開狀態持久化 (LocalStorage)
- 修復子選單縮排與顏色問題

app/Http/Controllers/Admin/AuditController.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace App\Http\Controllers\Admin;
+
+use App\Http\Controllers\Controller;
+use Illuminate\Http\Request;
+
+class AuditController extends Controller
+{
+    // 採購單稽核
+    public function purchases()
+    {
+        return view('admin.placeholder', [
+            'title' => '採購單稽核',
+            'description' => '採購單審核流程',
+        ]);
+    }
+
+    // 調撥單稽核
+    public function transfers()
+    {
+        return view('admin.placeholder', [
+            'title' => '調撥單稽核',
+            'description' => '調撥單審核流程',
+        ]);
+    }
+
+    // 補貨單稽核
+    public function replenishments()
+    {
+        return view('admin.placeholder', [
+            'title' => '補貨單稽核',
+            'description' => '補貨單審核流程',
+        ]);
+    }
+}