feat(ui): UI/交互优化 — 动画系统+Design Token+骨架屏+微反馈

1. Design Token 统一：CategoryIcon/BudgetBar/Numpad/Skeleton/TransactionItem
   硬编码hex颜色替换为 $primary/$border/$danger 等SCSS变量
2. 入场动画：mixins.scss 添加 fade-in-up/bounce-in/count-up 等 mixin+keyframes，
   首页卡片/金额/快捷按钮应用交错入场动画
3. 记账成功动画增强：SaveSuccess 增加纸屑粒子爆发+光环脉冲效果，
   prefers-reduced-motion 下自动隐藏
4. 骨架屏替代文字加载：recurring/group-manage/notifications 三个页面
   从"加载中..."替换为骨架屏；空状态增加图标容器+引导文案
5. 交互微反馈：分类按压0.92缩放、推荐虚线呼吸动画、
   Tab滑块cubic-bezier优化、快捷按钮弹性按压
6. 左滑删除提示：TransactionItem首项1.5s后自动微微左滑再回弹，
   引导用户发现滑动删除功能

client/src/pages/add/index.vue

@@ -328,7 +328,11 @@ function goBack() {
 
 .title { font-size: $font-xl; font-weight: 500; color: $text; }
 
-.type-toggle-wrap { display: flex; justify-content: center; margin: $space-sm 0; }
+.type-toggle-wrap {
+  display: flex; justify-content: center;
+  margin: $space-sm 0;
+  @include fade-in-up;
+}
 
 .type-toggle {
   display: inline-flex;
@@ -363,7 +367,7 @@ function goBack() {
   background: $surface;
   border-radius: $radius-lg;
   box-shadow: $shadow-sm;
-  transition: transform $transition-normal;
+  transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
 }
 
 .income .slider { transform: translateX(160rpx); }
@@ -387,8 +391,9 @@ function goBack() {
   gap: 6rpx;
   padding: 12rpx 0;
   position: relative;
+  -webkit-tap-highlight-color: transparent;
 
-  &:active { transform: scale(0.95); }
+  &:active { transform: scale(0.92); }
 
   &.suggested {
     .cat-icon-wrap {
@@ -396,10 +401,16 @@ function goBack() {
       border-radius: $radius-lg;
       padding: 6rpx;
       margin: -6rpx;
+      animation: suggest-pulse 2s ease-in-out infinite;
     }
   }
 }
 
+@keyframes suggest-pulse {
+  0%, 100% { border-color: $primary; }
+  50% { border-color: lighten($primary, 30%); }
+}
+
 .cat-icon-wrap {
   position: relative;
   transition: all $transition-normal;