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/hooks/useThemeScheduler.ts

@@ -0,0 +1,18 @@
+import { useEffect, useState } from 'react';
+import { useThemeStore, getScheduledTheme } from '../store/themeStore';
+
+export function useThemeScheduler(): string {
+  const state = useThemeStore();
+  const [effectiveTheme, setEffectiveTheme] = useState(() => getScheduledTheme(state));
+
+  useEffect(() => {
+    setEffectiveTheme(getScheduledTheme(useThemeStore.getState()));
+    if (!state.enableThemeScheduler) return;
+    const id = setInterval(() => {
+      setEffectiveTheme(getScheduledTheme(useThemeStore.getState()));
+    }, 60_000);
+    return () => clearInterval(id);
+  }, [state.enableThemeScheduler, state.theme, state.themeDay, state.themeNight, state.timeDayStart, state.timeNightStart]);
+
+  return effectiveTheme;
+}