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/app/layout.tsx

@@ -83,6 +83,8 @@ export default async function RootLayout({
   const settings = await getPublicSettingsCached();
   const accent = settings.accent;
   const accentCSS = accentStyleCSS(accent || "");
+  const customCSS = (settings.custom_css || "").trim();
+  const customJS = (settings.custom_js || "").trim();
   const motionCfg = motionConfigFromSettings(settings);
   const motionHtmlClass = [
     !motionCfg.ui_animations ? "j13-reduce-motion" : "",
@@ -117,6 +119,13 @@ export default async function RootLayout({
             dangerouslySetInnerHTML={{ __html: accentCSS }}
           />
         ) : null}
+        {customCSS ? (
+          <style
+            id="j13-custom-css"
+            data-custom-css-source="ssr"
+            dangerouslySetInnerHTML={{ __html: customCSS }}
+          />
+        ) : null}
         <a href="#main" className="skip-link">
           跳到主要内容
         </a>
@@ -147,9 +156,12 @@ export default async function RootLayout({
         <Toaster />
         <TipHost />
         <AccountGuard />
-        <ThemeSync initialAccent={accent || ""} />
+        <ThemeSync initialAccent={accent || ""} initialCustomCSS={customCSS} />
         <VisitBeacon />
         <RealtimeProvider userId={user ? user.id : null} />
+        {customJS ? (
+          <script id="j13-custom-js" dangerouslySetInnerHTML={{ __html: customJS }} />
+        ) : null}
       </body>
     </html>
   );