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/compose/page.tsx

@@ -2,8 +2,6 @@
 
 import { useEffect, useState, Suspense } from "react";
 import { useRouter, useSearchParams } from "next/navigation";
-import Link from "next/link";
-import { ChevronRight } from "lucide-react";
 import { apiMe } from "@/lib/api";
 import PostComposer from "@/components/PostComposer";
 
@@ -30,7 +28,7 @@ function ComposeInner() {
 
   if (!ready) {
     return (
-      <div className="j13-compose-stage px-8 py-16 text-center">
+      <div className="j13-compose-stage is-studio px-8 py-16 text-center">
         <p className="meta">正在准备发帖…</p>
       </div>
     );
@@ -42,17 +40,9 @@ function ComposeInner() {
 export default function ComposePage() {
   return (
     <div className="j13-compose-page">
-      <nav className="meta -mt-4 sm:-mt-6 mb-1.5 flex items-center gap-1 text-[12.5px] leading-none shrink-0">
-        <Link href="/" className="hover:text-[var(--accent)] transition-colors">
-          首页
-        </Link>
-        <ChevronRight size={13} />
-        <span style={{ color: "var(--ink-2)" }}>发布新帖</span>
-      </nav>
-
       <Suspense
         fallback={
-          <div className="j13-compose-stage px-8 py-16 text-center">
+          <div className="j13-compose-stage is-studio px-8 py-16 text-center">
             <p className="meta">正在准备发帖…</p>
           </div>
         }