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/chat/ChatShell.tsx

@@ -419,7 +419,7 @@ export default function ChatShell({
           </h1>
           <button
             onClick={() => setShowCreate(true)}
-            className="w-8 h-8 flex items-center justify-center rounded-full hover:bg-[var(--accent-soft)] transition-colors"
+            className="w-8 h-8 flex items-center justify-center rounded-full hover:bg-[var(--panel-2)] transition-colors"
             style={{ color: "var(--accent)" }}
             aria-label="新建群聊"
             data-tip="新建群聊"
@@ -452,7 +452,7 @@ export default function ChatShell({
                   setQuery("");
                 }}
                 aria-label="清除搜索"
-                className="w-5 h-5 flex items-center justify-center rounded-full hover:bg-[var(--accent-soft)] shrink-0"
+                className="w-5 h-5 flex items-center justify-center rounded-full hover:bg-[var(--panel-2)] shrink-0"
                 style={{ color: "var(--ink-3)" }}
               >
                 <X size={12} />
@@ -484,7 +484,7 @@ export default function ChatShell({
                   <button
                     key={u.id}
                     onClick={() => openDM(u.id)}
-                    className="w-full flex items-center gap-2.5 px-2.5 py-2 rounded-lg text-left hover:bg-[var(--accent-soft)] transition-colors"
+                    className="w-full flex items-center gap-2.5 px-2.5 py-2 rounded-lg text-left hover:bg-[var(--panel-2)] transition-colors"
                   >
                     <Avatar name={u.nickname || u.username} src={u.avatar || undefined} size={36} />
                     <div className="min-w-0">