feat(tokens): add missing variables to uni.scss

- $font-size-xxs (18rpx), $font-size-4xl (64rpx)
- $uv-placeholder-color (#999999)
- Semantic colors: $color-price, $color-status-*
- Change $font-family-body to system fonts

src/uni.scss

@@ -49,6 +49,7 @@ $color-error: $uv-error;
 $uv-main-color: #111111;
 $uv-content-color: #333333;
 $uv-tips-color: #666666;
+$uv-placeholder-color: #999999;
 $uv-light-color: #dadbde;
 $uv-disabled-color: #c8c9cc;
 $uv-bg-color: #f3f4f6;
@@ -66,12 +67,20 @@ $color-ring: $uv-primary;
 // Gradients
 $gradient-accent: linear-gradient(135deg, #{$uv-primary}, #{$uv-primary-dark});
 
+// Semantic colors (价格/状态)
+$color-price: $uv-error;
+$color-price-highlight: #FFD600;
+$color-status-pending: #ff9500;
+$color-status-success: #00b42a;
+$color-status-cancel: #86909c;
+
 // === TYPOGRAPHY ===
 
 $font-family-display: 'SourceHanSerifCN', '思源宋体', serif;
-$font-family-body: 'SourceHanSerifCN', '思源宋体', -apple-system, 'PingFang SC', sans-serif;
+$font-family-body: -apple-system, 'PingFang SC', 'Helvetica Neue', sans-serif;
 $font-family-mono: 'Menlo', 'Monaco', 'Courier New', monospace;
 
+$font-size-xxs: 18rpx;
 $font-size-xs: 20rpx;
 $font-size-sm: 24rpx;
 $font-size-base: 28rpx;
@@ -80,6 +89,7 @@ $font-size-xl: 36rpx;
 $font-size-title: 38rpx;
 $font-size-2xl: 44rpx;
 $font-size-3xl: 56rpx;
+$font-size-4xl: 64rpx;
 $font-size-display: 72rpx;
 
 $font-weight-normal: 400;