feat: add help guide, skills marketplace, and contact page to website

- Add guide.html: full help documentation with sidebar navigation
  (快速开始/接入平台/模型配置/技能/常见问题/官方文档)
  includes 39 curated Chinese skills, embedded WeChat QR for offline use
- Add skills.html: skills marketplace page with search, category filter,
  and one-click install commands for 6 Chinese social platforms
- Update index.html: add guide entry button in hero and footer

website/index.html

@@ -305,6 +305,10 @@
             <span class="zh">⭐ GitHub 开源</span>
             <span class="en hidden">⭐ GitHub</span>
         </a>
+        <a href="guide.html" class="btn btn-outline">
+            <span class="zh">📖 使用指南</span>
+            <span class="en hidden">📖 Guide</span>
+        </a>
     </div>
 
     <div class="stats">
@@ -621,6 +625,7 @@
     </p>
     <p style="margin-top: 8px;">
         <a href="https://github.com/dongsheng123132/u-claw">GitHub</a> ·
+        <a href="guide.html">使用指南</a> ·
         <a href="https://github.com/openclaw/openclaw">OpenClaw</a> ·
         <a href="mailto:hefangsheng@gmail.com">hefangsheng@gmail.com</a>
     </p>