refactor(settings): interface scale as a segmented picker (#1197)

Replace the Interface Scale zoom slider and its tick row with the shared
SettingsSegmented control — one button per preset (80–150%), matching the
Lyrics, Queue and Track-transitions sections. Drops the slider/tick
alignment issue entirely. Legacy off-preset values snap to the nearest
preset so one button is always active. Removes the now-dead slider CSS.

src/styles/components/ui-scale-slider.css

@@ -1,31 +1,3 @@
-/* ─── 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);
-}
-
 /* ── Folder Browser (Miller Columns) ──────────────────────────────────────── */
 
 .folder-browser {