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/de.ts

@@ -574,6 +574,15 @@ export const deTranslation = {
     seekbarParticletrail: 'Partikel-Spur',
     seekbarLiquidfill: 'Flüssigkeit',
     seekbarRetrotape: 'Retro-Band',
+    themeSchedulerTitle: 'Theme-Zeitplan',
+    themeSchedulerEnable: 'Theme-Zeitplan aktivieren',
+    themeSchedulerEnableSub: 'Wechselt automatisch zwischen zwei Themes basierend auf der Uhrzeit',
+    themeSchedulerDayTheme: 'Tages-Theme',
+    themeSchedulerDayStart: 'Tag beginnt um',
+    themeSchedulerNightTheme: 'Nacht-Theme',
+    themeSchedulerNightStart: 'Nacht beginnt um',
+    uiScaleTitle: 'Interface-Skalierung',
+    uiScaleLabel: 'Zoom',
   },
   changelog: {
     modalTitle: 'Was ist neu',