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/en.ts

@@ -575,6 +575,15 @@ export const enTranslation = {
     seekbarParticletrail: 'Particle Trail',
     seekbarLiquidfill: 'Liquid Fill',
     seekbarRetrotape: 'Retro Tape',
+    themeSchedulerTitle: 'Auto-Switch Theme',
+    themeSchedulerEnable: 'Enable Theme Scheduler',
+    themeSchedulerEnableSub: 'Automatically switch between two themes based on the time of day',
+    themeSchedulerDayTheme: 'Day Theme',
+    themeSchedulerDayStart: 'Day Starts At',
+    themeSchedulerNightTheme: 'Night Theme',
+    themeSchedulerNightStart: 'Night Starts At',
+    uiScaleTitle: 'Interface Scale',
+    uiScaleLabel: 'Zoom',
   },
   changelog: {
     modalTitle: "What's New",