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/styles/components.css

@@ -6739,3 +6739,31 @@
   align-items: center;
   gap: 0.5rem;
 }
+
+/* ─── UI Scale Slider ─── */
+.ui-scale-slider {
+  -webkit-appearance: none;
+  appearance: none;
+  width: 100%;
+  height: 4px;
+  border-radius: 2px;
+  background: var(--border-subtle);
+  outline: none;
+  cursor: pointer;
+}
+
+.ui-scale-slider::-webkit-slider-thumb {
+  -webkit-appearance: none;
+  appearance: none;
+  width: 16px;
+  height: 16px;
+  border-radius: 50%;
+  background: var(--accent);
+  cursor: pointer;
+  transition: transform 0.1s ease, box-shadow 0.1s ease;
+}
+
+.ui-scale-slider::-webkit-slider-thumb:hover {
+  transform: scale(1.2);
+  box-shadow: 0 0 0 4px color-mix(in srgb, var(--accent) 20%, transparent);
+}