feat(site): add docs.html, update demo and index for v0.1.3

- docs.html: comprehensive single-page documentation with sidebar navigation
  covering all APIs, config, events, plugins, themes, i18n, and syntax reference
- demo.html: add readOnly toggle, emoji/new syntax demo content,
  imagePaste plugin, refresh API button, docs link
- index.html: add docs link to nav and footer

site/index.html

@@ -386,13 +386,14 @@
 	      <span class="logo-mark" title="MetonaEditor" aria-label="MetonaEditor Logo"><svg viewBox="0 0 24 24" width="16" height="16" fill="none" stroke="white" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round"><path d="M5 19V6l7 8 7-8v13"/></svg></span>
 	      MetonaEditor
 	    </a>
-	    <div class="nav-links">
-      <a href="#features">特性</a>
-      <a href="#demo">体验</a>
-      <a href="#api">API</a>
-      <a href="#shortcuts">快捷键</a>
-      <a class="nav-cta" href="demo.html">在线演示</a>
-    </div>
+		    <div class="nav-links">
+	      <a href="#features">特性</a>
+	      <a href="#demo">体验</a>
+	      <a href="#api">API</a>
+	      <a href="#shortcuts">快捷键</a>
+	      <a href="docs.html">文档</a>
+	      <a class="nav-cta" href="demo.html">在线演示</a>
+	    </div>
   </div>
 </nav>
 
@@ -668,12 +669,13 @@
 
 <footer>
   <div class="container">
-    <div class="footer-links">
-      <a href="demo.html">在线演示</a>
-      <a href="https://git.metona.cn/MetonaTeam/-/packages/npm/@metona-team%2Fmetona-editor" target="_blank" rel="noopener">npm</a>
-      <a href="https://git.metona.cn/MetonaTeam/MetonaEditor" target="_blank" rel="noopener">源码仓库</a>
-      <a href="https://git.metona.cn/MetonaTeam/MetonaEditor/issues" target="_blank" rel="noopener">问题反馈</a>
-    </div>
+	    <div class="footer-links">
+	      <a href="demo.html">在线演示</a>
+	      <a href="docs.html">文档</a>
+	      <a href="https://git.metona.cn/MetonaTeam/-/packages/npm/@metona-team%2Fmetona-editor" target="_blank" rel="noopener">npm</a>
+	      <a href="https://git.metona.cn/MetonaTeam/MetonaEditor" target="_blank" rel="noopener">源码仓库</a>
+	      <a href="https://git.metona.cn/MetonaTeam/MetonaEditor/issues" target="_blank" rel="noopener">问题反馈</a>
+	    </div>
     <div>MetonaEditor · MIT License · 由 <a href="https://git.metona.cn/MetonaTeam" target="_blank" rel="noopener">Metona Team</a> 出品</div>
   </div>
 </footer>