refactor: UI/UX 全面重构 — 设计系统统一

设计系统：
- uni.scss 扩展：间距/圆角/字体/阴影/动画 token 体系
- 新建 styles/mixins.scss：20+ 公共 mixin

页面重构（12 个页面）：
- 首页/记账/统计/账单/个人中心/预算/分类管理
- 群组管理/通知中心/管理员/用户管理/编辑资料

所有硬编码替换为设计 token：
- 颜色：#FFF8F0→$bg, #FFFFFF→$surface, #FF8C69→$primary 等
- 间距：40rpx→$space-xl, 24rpx→$space-md 等
- 字体：28rpx→$font-lg, 24rpx→$font-md 等
- 圆角：20rpx→$radius-lg, 40rpx→$radius-2xl 等
- 阴影：统一使用 $shadow-md/$shadow-sm

重复样式提取为 mixin：
- page-base, sticky-header, nav-bar, card, modal-mask
- tabs, tab, state-box, shimmer, flex-center 等

client/src/pages/profile-edit/index.vue

@@ -105,43 +105,34 @@ async function saveProfile() {
 </script>
 
 <style lang="scss" scoped>
+@import '@/styles/mixins.scss';
+
 .page {
-  min-height: 100vh;
-  background: #FFF8F0;
-  padding: 0 0 180rpx;
+  @include page-base;
 }
 
 .header-fixed {
-  position: sticky;
-  top: 0;
-  z-index: 100;
-  background: #FFF8F0;
+  @include sticky-header;
 }
 
-.status-bar { background: #FFF8F0; }
+.status-bar { @include status-bar; }
 
 .nav-bar {
   display: flex;
   align-items: center;
-  padding: 16rpx 40rpx 24rpx;
+  padding: $space-sm $space-xl $space-md;
 }
 
 .nav-back {
-  width: 88rpx;
-  height: 88rpx;
-  display: flex;
-  align-items: center;
-  justify-content: center;
-
-  &:active { opacity: 0.6; }
+  @include nav-back;
 }
 
 .nav-title {
   flex: 1;
   text-align: center;
-  font-size: 36rpx;
+  font-size: $font-2xl;
   font-weight: 600;
-  color: #2D1B1B;
+  color: $text;
 }
 
 .nav-save {
@@ -155,16 +146,16 @@ async function saveProfile() {
 }
 
 .save-text {
-  font-size: 28rpx;
+  font-size: $font-lg;
   font-weight: 600;
-  color: #FF8C69;
+  color: $primary;
 }
 
 .avatar-section {
   display: flex;
   flex-direction: column;
   align-items: center;
-  padding: 48rpx 0 32rpx;
+  padding: $space-2xl 0 $space-lg;
 }
 
 .avatar-wrap {
@@ -172,7 +163,7 @@ async function saveProfile() {
   height: 160rpx;
   border-radius: 50%;
   border: 6rpx solid rgba(255, 255, 255, 0.5);
-  background: linear-gradient(135deg, #FF8C69, #FFB89A);
+  background: linear-gradient(135deg, $primary, #FFB89A);
   display: flex;
   align-items: center;
   justify-content: center;
@@ -196,61 +187,61 @@ async function saveProfile() {
 }
 
 .avatar-hint {
-  font-size: 24rpx;
-  color: #BFB3B3;
-  margin-top: 16rpx;
+  font-size: $font-md;
+  color: $text-muted;
+  margin-top: $space-sm;
 }
 
 .form-card {
-  margin: 32rpx 40rpx 0;
-  background: #FFFFFF;
-  border-radius: 40rpx;
-  border: 2rpx solid #F0E0D6;
-  box-shadow: 4rpx 4rpx 12rpx rgba(45, 27, 27, 0.08);
+  margin: $space-lg $space-xl 0;
+  background: $surface;
+  border-radius: $radius-2xl;
+  border: 2rpx solid $border;
+  box-shadow: $shadow-md;
   overflow: hidden;
 }
 
 .form-item {
   display: flex;
   align-items: center;
-  padding: 32rpx 40rpx;
+  padding: $space-lg $space-xl;
 }
 
 .form-label {
   width: 120rpx;
-  font-size: 28rpx;
+  font-size: $font-lg;
   font-weight: 500;
-  color: #2D1B1B;
+  color: $text;
   flex-shrink: 0;
 }
 
 .form-input {
   flex: 1;
-  font-size: 28rpx;
-  color: #2D1B1B;
+  font-size: $font-lg;
+  color: $text;
 }
 
 .tips-card {
-  margin: 32rpx 40rpx 0;
-  padding: 32rpx 40rpx;
-  background: #FFFFFF;
-  border-radius: 40rpx;
-  border: 2rpx solid #F0E0D6;
-  box-shadow: 4rpx 4rpx 12rpx rgba(45, 27, 27, 0.08);
+  margin: $space-lg $space-xl 0;
+  padding: $space-lg $space-xl;
+  background: $surface;
+  border-radius: $radius-2xl;
+  border: 2rpx solid $border;
+  box-shadow: $shadow-md;
 }
 
 .tips-title {
-  font-size: 28rpx;
+  font-size: $font-lg;
   font-weight: 600;
-  color: #2D1B1B;
+  color: $text;
   display: block;
-  margin-bottom: 16rpx;
+  margin-bottom: $space-sm;
 }
 
 .tips-text {
-  font-size: 24rpx;
-  color: #8B7E7E;
+  font-size: $font-md;
+  color: $text-sec;
   display: block;
-  margin-bottom: 8rpx;
+  margin-bottom: $space-xs;
 }
 </style>