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/lib/api.ts

@@ -677,6 +677,10 @@ export interface PublicSettings {
   attachment_max_count: number;
   /** 正文插图上限 MB；缺省 5 */
   image_max_mb: number;
+  /** 全站自定义 CSS；空串=无 */
+  custom_css: string;
+  /** 全站自定义 JS；空串=无（保存后整页加载生效） */
+  custom_js: string;
 }
 
 /** 与后端 DefaultAttachmentExts 保持同步 */
@@ -711,6 +715,8 @@ const DEFAULT_PUBLIC_SETTINGS: PublicSettings = {
   attachment_max_mb: 20,
   attachment_max_count: 10,
   image_max_mb: 5,
+  custom_css: "",
+  custom_js: "",
 };
 
 function normalizeAttachmentExts(raw: unknown): string[] {
@@ -780,6 +786,8 @@ function normalizePublicSettings(data: Partial<PublicSettings> | null | undefine
     attachment_max_mb: maxMB,
     attachment_max_count: maxCount,
     image_max_mb: imageMB,
+    custom_css: typeof data?.custom_css === "string" ? data.custom_css : "",
+    custom_js: typeof data?.custom_js === "string" ? data.custom_js : "",
   };
 }
 
@@ -2136,6 +2144,8 @@ export type UpdateSiteSettingsBody = {
   attachment_max_mb?: number;
   attachment_max_count?: number;
   image_max_mb?: number;
+  custom_css?: string;
+  custom_js?: string;
   timeline_git_import?: string;
 };