feat: 帖子收藏与用户关注

- 新增收藏功能：favorite 服务与 handler、FavoriteButton 组件
- 新增关注功能：follow 服务与 handler、FollowButton 组件
- 用户主页适配关注/粉丝与收藏展示
- flash 消息工具、广告与侧边栏组件微调

frontend/components/BadgeChip.tsx

@@ -22,11 +22,11 @@ export default function BadgeChip({
 
   return (
     <span
-      className={`inline-flex items-center gap-1 rounded-full px-2 py-0.5 text-[11px] font-medium leading-[1.6] whitespace-nowrap select-none ${className}`}
+      className={`inline-flex items-center gap-1.5 rounded-full px-2.5 py-1 text-[11.5px] font-medium leading-[1.5] whitespace-nowrap select-none transition-transform duration-200 hover:-translate-y-[1px] ${className}`}
       style={{ background: soft, color }}
       data-tip={tip ?? badge.name}
     >
-      <Icon size={11} className="shrink-0" />
+      <Icon size={12} className="shrink-0" />
       {badge.name}
     </span>
   );