refactor(static): 首页内联样式解耦至 css/index.css

- 新增页面级样式文件 css/index.css（与 view.css/aibox.css 惯例一致）
- index.html 移除内联 <style> 块与头像内联样式，改为外链
- 头像圆角 100px 优化为 border-radius: 50%

static/public/css/index.css

@@ -0,0 +1,38 @@
+/* index.css — 社区首页专属样式（通用主题见 theme.css） */
+
+body {
+    align-items: normal;
+}
+
+/* ===== 头部 ===== */
+.header {
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+    width: 100%;
+}
+
+.right-group {
+    display: flex;
+    align-items: center;
+}
+
+.right-group > img,
+.right-group > b,
+.right-group > button {
+    margin-left: 5px;
+    margin-right: 5px;
+}
+
+#avatar {
+    border-radius: 50%;
+}
+
+/* ===== 网站简介 ===== */
+.site-intro {
+    max-width: 640px;
+    margin: 0 auto;
+    font-size: 0.95rem;
+    line-height: 1.9;
+    color: var(--fg-secondary);
+}

static/public/index.html

@@ -4,41 +4,14 @@
     <meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <link rel="stylesheet" href="css/theme.css">
-    <style>
-        body {
-            align-items: normal;
-        }
-        .header {
-            display: flex;
-            justify-content: space-between;
-            align-items: center;
-            width: 100%;
-        }
-        .right-group {
-            display: flex;
-            align-items: center;
-        }
-        .right-group > img,
-        .right-group > b,
-        .right-group > button {
-            margin-left: 5px;
-            margin-right: 5px;
-        }
-        .site-intro {
-            max-width: 640px;
-            margin: 0 auto;
-            font-size: 0.95rem;
-            line-height: 1.9;
-            color: var(--fg-secondary);
-        }
-    </style>
+    <link rel="stylesheet" href="css/index.css">
     <title>DNFS 欢迎来到树状笔记</title>
 </head>
 <body>
     <header class="header">
         <h1 onclick="window.location.href='index.html'">DNFS 树状笔记</h1>
         <div class="right-group">
-            <img src="favicon.ico" alt="头像加载失败" id="avatar" width="70px" height="70px" style="border-radius: 100px;">
+            <img src="favicon.ico" alt="头像加载失败" id="avatar" width="70px" height="70px">
             <b id="name">DNFS</b>
             <button id="enterBtn" onclick="window.location.href='dnfs.html'" style="display:none">进入笔记</button>
             <button id="logoutBtn" style="display:none">退出</button>