docs: add comprehensive README.md and fix bugs

- add README.md with usage and deployment guide
- fix category sync logic in backend
- fix URL overflow in admin services list
- fix data caching issues in front-end and back-end
- add 'View Front-end' button in admin dashboard

templates/admin/categories.html

@@ -10,7 +10,10 @@
             <h1>📂 分类管理</h1>
             <a href="/admin" class="back-link">← 返回首页</a>
         </div>
-        <button class="btn btn-primary" onclick="showCreateModal()">+ 新建分类</button>
+        <div class="header-right">
+            <button class="btn btn-outline" onclick="window.open('/', '_blank')" style="margin-right: 10px;">查看前台 ↗</button>
+            <button class="btn btn-primary" onclick="showCreateModal()">+ 新建分类</button>
+        </div>
     </div>
 
     <!-- 分类列表 -->
@@ -272,6 +275,17 @@
         gap: 10px;
     }
 
+    .btn-outline {
+        background: transparent;
+        border: 1px solid rgba(255,255,255,0.3);
+        color: #fff;
+    }
+
+    .btn-outline:hover {
+        background: rgba(255,255,255,0.1);
+        border-color: #fff;
+    }
+
     .btn {
         padding: 10px 20px;
         border: none;