feat: 外观支持自定义 CSS/JS，并升级发帖工作台与积分存量看板

后台可注入全站 CSS/JS（SSR 生效，CSS 可热换）；发帖/编辑改为锁一屏工作室；经济看板增加存量健康度；主题令牌与弹层误关一并收紧。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/components/SiteChrome.tsx

@@ -17,6 +17,11 @@ function pathIsChat(pathname: string | null) {
   return pathname === "/chat" || pathname.startsWith("/chat/");
 }
 
+function pathIsComposeStudio(pathname: string | null) {
+  if (!pathname) return false;
+  return pathname === "/compose" || /^\/post\/[^/]+\/edit\/?$/.test(pathname);
+}
+
 /** 帖子详情（非 edit）移动端有底栏，回顶需抬高 */
 function pathIsPostDetail(pathname: string | null) {
   if (!pathname) return false;
@@ -75,8 +80,8 @@ export default function SiteChrome({
     return <>{children}</>;
   }
 
-  // 聊天页锁视口、主滚动在对话区，窗口回顶无意义
-  const showBackToTop = !pathIsChat(pathname);
+  // 聊天 / 发帖工作台锁视口，窗口回顶无意义
+  const showBackToTop = !pathIsChat(pathname) && !pathIsComposeStudio(pathname);
 
   return (
     <>