feat(ui): 记录页月份联动与多项 UI 美化/修复

- records: 底部列表与月份选择器联动，新增 [本月|最近] 分段控件；标题/空态随模式切换
- leaderboard: 领奖台布局(冠军居中+皇冠)、次数标注于底座且三档水平对齐；头像 cloud:// 批量预解析提速(云函数需重新部署)
- index/timer: 主色底图标改白色变体修复隐形；目标数字按微信字体缩放补偿真机遮挡
- settings: 配色方案横滑渐变色卡；头像上传前压缩至 200px
- theme: 新增 teal 主题；暗黑背景统一对齐
- 圆形头像双保险(image 自身 border-radius)修复月/年榜方图

注: cloudfunctions/leaderboard 改动须在开发者工具重新部署才生效。

components/ui-card/ui-card.wxss

@@ -7,6 +7,14 @@
   box-sizing: border-box;
 }
 
+/* Dark mode: shadows barely read against the darker backdrop, so add a
+   faint bright edge to keep cards elevated and separated from the page. */
+@media (prefers-color-scheme: dark) {
+  .ui-card {
+    box-shadow: 0 4rpx 20rpx rgba(0, 0, 0, 0.45), 0 0 0 1rpx rgba(255, 255, 255, 0.04);
+  }
+}
+
 .ui-card--flush {
   padding: 0;
 }
@@ -18,6 +26,21 @@
   border-radius: 20rpx;
 }
 
+/* Gradient variant: hero card filled with the theme gradient, white text.
+   Descendant elements override --text / --text-secondary locally so any
+   generic text inside automatically flips to white. */
+.ui-card.gradient {
+  background: linear-gradient(135deg, var(--primary) 0%, var(--primary-light) 100%);
+  box-shadow: 0 8rpx 28rpx rgba(var(--primary-rgb), 0.35);
+  /* These custom properties are the ONLY channel that crosses the component
+     style-isolation boundary into slotted page content (see MEMORY.md). Any
+     text/fill inside the hero card must read from them, never var(--primary). */
+  --text: #FFFFFF;
+  --text-secondary: rgba(255, 255, 255, 0.85);
+  --border: rgba(255, 255, 255, 0.28);
+  --on-primary: #FFFFFF;
+}
+
 /* Staggered entrance animation */
 .ui-card.in {
   animation: uiCardIn 0.45s ease both;