refactor(settings): G.55 — extract helpers + credits + tab index (#620)

Pull pure helpers, the contributors/maintainers data list and the
tab type/search index out of `Settings.tsx` so the main component
only has tab-section render logic + the orchestrating state left:

- `utils/audioDeviceLabels.ts` — five ALSA-device label helpers
  (formatAudioDeviceLabel + duplicate-disambiguation + sort +
  select-option builder).
- `utils/formatBytes.ts` — formatBytes + snapHotCacheMb.
- `components/settings/LoudnessLufsButtonGroup.tsx` — small chip
  group used by the audio tab.
- `components/settings/settingsTabs.ts` — `Tab` type + legacy alias
  map + `resolveTab` + `SearchIndexEntry` + `SETTINGS_INDEX` + the
  `matchScore` substring-with-fuzzy-fallback scorer.
- `config/settingsCredits.ts` — `CONTRIBUTORS` (~270 LOC of static
  contributor history) + `MAINTAINERS`.

Pure code-move. Settings.tsx: 3552 → 3037 LOC (−515). Settings/G
journey now 5298 → 3037 LOC (~43% reduction).

src/components/settings/LoudnessLufsButtonGroup.tsx

@@ -0,0 +1,24 @@
+import type { LoudnessLufsPreset } from '../../store/authStoreTypes';
+
+const LOUDNESS_LUFS_BUTTON_ORDER: LoudnessLufsPreset[] = [-10, -12, -14, -16];
+
+export function LoudnessLufsButtonGroup(props: {
+  value: LoudnessLufsPreset;
+  onSelect: (v: LoudnessLufsPreset) => void;
+}) {
+  return (
+    <div style={{ display: 'flex', alignItems: 'center', gap: '0.35rem', flexWrap: 'wrap' }}>
+      {LOUDNESS_LUFS_BUTTON_ORDER.map(v => (
+        <button
+          key={v}
+          type="button"
+          className={`btn ${props.value === v ? 'btn-primary' : 'btn-ghost'}`}
+          style={{ fontSize: 12, padding: '3px 12px' }}
+          onClick={() => props.onSelect(v)}
+        >
+          {v}
+        </button>
+      ))}
+    </div>
+  );
+}