feat(settings): theme scheduler, UI scale, CustomSelect scroll fix

- Time-based theme scheduler: auto-switches between day/night theme
  based on configurable times; setInterval re-checks every minute
- UI scale slider (80–150%) via CSS zoom on document root; preset
  buttons aligned to actual slider positions
- CustomSelect: scroll listener keeps dropdown anchored on scroll
- All features i18n in 7 languages

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/locales/zh.ts

@@ -568,6 +568,15 @@ export const zhTranslation = {
     seekbarParticletrail: '粒子轨迹',
     seekbarLiquidfill: '液体填充',
     seekbarRetrotape: '复古磁带',
+    themeSchedulerTitle: '主题定时切换',
+    themeSchedulerEnable: '启用主题定时器',
+    themeSchedulerEnableSub: '根据一天中的时间自动在两个主题之间切换',
+    themeSchedulerDayTheme: '白天主题',
+    themeSchedulerDayStart: '白天开始时间',
+    themeSchedulerNightTheme: '夜晚主题',
+    themeSchedulerNightStart: '夜晚开始时间',
+    uiScaleTitle: '界面缩放',
+    uiScaleLabel: '缩放',
   },
   changelog: {
     modalTitle: '新功能',