feat(chat): 页面级 basePath 引导（路径模式静态面）

Co-Authored-By: Claude Code <noreply@anthropic.com>

static/chat.html

@@ -4,13 +4,42 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no">
     <title>AI Support</title>
-    <link rel="stylesheet" href="/static/css/style.css">
-    <script src="/static/js/theme.js"></script>
+    <script>
+    (function () {
+        /* spec 2026-10-19 §4:路径前缀模式(/t/<slug>/)按当前地址推导基础路径;
+           Host 模式(根路径 "/")推导为空串——全部引用零变化。
+           拼接安全:match 命中即字符集白名单([a-z0-9-]),base 只做 URL 属性
+           赋值,绝不拼 HTML(防线 §2/§3);找不到标记(如 /admin 域)同样得空串。 */
+        var m = location.pathname.match(/^\/t\/[a-z0-9-]+\/$/);
+        var base = m ? location.pathname.slice(0, -1) : "";
+        window.__BASE_PATH__ = base;
+        function css(href) {
+            var l = document.createElement("link");
+            l.rel = "stylesheet"; l.href = base + href;
+            document.head.appendChild(l);
+        }
+        function js(src) {
+            var s = document.createElement("script");
+            s.src = base + src; s.async = false; /* 保序:theme 先于 chat */
+            document.head.appendChild(s);
+        }
+        css("/static/css/style.css");
+        document.addEventListener("DOMContentLoaded", function () {
+            /* js 装载放 DOMContentLoaded:head 动态插入的 async=false 脚本与
+               解析进度无形式化顺序保证,且 chat.js 顶层有同步 DOM 查询——
+               DOM 就绪后装载与原 body 末尾形态等价且保序 */
+            js("/static/js/theme.js");
+            js("/static/js/chat.js");
+            var img = document.querySelector(".avatar-img");
+            if (img) img.src = base + "/api/public/avatar";
+        });
+    })();
+    </script>
 </head>
 <body>
     <div class="chat-container">
         <div class="chat-header">
-            <div class="avatar"><span class="avatar-emoji">🤖</span><img class="avatar-img" alt="" src="/api/public/avatar"></div>
+            <div class="avatar"><span class="avatar-emoji">🤖</span><img class="avatar-img" alt=""></div>
             <div class="info">
                 <h1>AI Support</h1>
                 <div class="availability">Online now - Usually replies in minutes</div>
@@ -76,7 +105,5 @@
         </div>
         <div class="chat-footer"><span class="footer-left">By chatting, you agree to our <a target="_blank" rel="noopener">privacy policy</a>.</span></div>
     </div>
-
-    <script src="/static/js/chat.js"></script>
 </body>
 </html>