add official Chrome feature demos

public/demo/webmcp/index.html

@@ -14,6 +14,7 @@
       </div>
       <div class="runtime">
         <span id="native-status" class="pill">检测中</span>
+        <a class="demo-home" href="../index.html">Demo 总览</a>
         <a href="https://developer.chrome.com/docs/ai/webmcp" target="_blank" rel="noreferrer">Chrome 官方文档</a>
       </div>
     </header>

public/demo/webmcp/styles.css

@@ -80,11 +80,24 @@ h2 {
 
 .runtime {
   display: flex;
+  flex-wrap: wrap;
   align-items: center;
   gap: 14px;
   margin-bottom: 8px;
 }
 
+.demo-home {
+  border: 1px solid var(--line);
+  background: var(--paper);
+  padding: 6px 10px;
+  color: var(--ink);
+}
+
+.demo-home:hover {
+  border-color: var(--blue);
+  background: #eef4ff;
+}
+
 .pill,
 .mode {
   display: inline-flex;