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/utils/audioDeviceLabels.ts

@@ -0,0 +1,118 @@
+/** Makes raw ALSA device names more readable on Linux.
+ *  Values are kept as-is (rodio needs the ALSA name); only the displayed label is cleaned.
+ *  e.g. "sysdefault:CARD=U192k" → "U192k"
+ *       "hw:CARD=U192k,DEV=0"   → "U192k (hw · PCM 0)"
+ *       "hdmi:CARD=NVidia,DEV=1" → "NVidia (HDMI · DEV 1)"  (same DEV as in ALSA string)
+ *       "iec958:CARD=PCH,DEV=0" → "PCH (S/PDIF)"
+ *  Names without ALSA prefix (pipewire, pulse, default…) are returned unchanged. */
+export function formatAudioDeviceLabel(name: string): string {
+  const cardMatch = name.match(/CARD=([^,]+)/);
+  if (!cardMatch) return name;
+  const card = cardMatch[1];
+  const devM = name.match(/DEV=(\d+)/);
+  const devNum = devM ? parseInt(devM[1], 10) : null;
+  const subM = name.match(/SUBDEV=(\d+)/);
+  const subNum = subM ? parseInt(subM[1], 10) : null;
+
+  if (name.startsWith('iec958:')) return `${card} (S/PDIF)`;
+  if (name.startsWith('hdmi:')) {
+    const d = devNum !== null ? devNum : 0;
+    return `${card} (HDMI · DEV ${d})`;
+  }
+  if (name.startsWith('sysdefault:')) {
+    if (devNum !== null && devNum > 0) return `${card} (default · PCM ${devNum})`;
+    return card;
+  }
+  if (name.startsWith('plughw:')) {
+    if (devNum !== null) {
+      const sub = subNum !== null ? ` · sub ${subNum}` : '';
+      return `${card} (plug · PCM ${devNum}${sub})`;
+    }
+    return card;
+  }
+  if (name.startsWith('hw:')) {
+    if (devNum !== null) {
+      const sub = subNum !== null ? ` · sub ${subNum}` : '';
+      return `${card} (hw · PCM ${devNum}${sub})`;
+    }
+    return `${card} (hw)`;
+  }
+  if (name.startsWith('front:')) return `${card} (Front)`;
+  if (name.startsWith('surround')) return `${card} (${name.split(':')[0]})`;
+  // Other ALSA iface:card,dev — show plugin + PCM so identical cards differ
+  const iface = name.split(':')[0];
+  if (iface && !['default', 'pulse', 'pipewire'].includes(iface)) {
+    if (devNum !== null) return `${card} (${iface} · PCM ${devNum})`;
+    return `${card} (${iface})`;
+  }
+  return card;
+}
+
+/** Readable tail when two devices still share the same label (rare after formatAudioDeviceLabel). */
+export function audioDeviceDuplicateHint(raw: string): string {
+  const cardM = raw.match(/CARD=([^,]+)/);
+  const devM = raw.match(/DEV=(\d+)/);
+  const subM = raw.match(/SUBDEV=(\d+)/);
+  const iface = raw.split(':')[0] || '';
+  const parts: string[] = [];
+  if (iface) parts.push(iface);
+  if (cardM) parts.push(cardM[1]);
+  if (devM) parts.push(`PCM ${devM[1]}`);
+  if (subM) parts.push(`sub ${subM[1]}`);
+  if (parts.length > 1) return parts.join(' · ');
+  return raw.length > 56 ? `…${raw.slice(-53)}` : raw;
+}
+
+/** When several devices share the same display label, append a disambiguator. */
+export function disambiguatedAudioDeviceLabel(raw: string, baseLabel: string, duplicateBase: boolean): string {
+  if (!duplicateBase) return baseLabel;
+  return `${baseLabel} · ${audioDeviceDuplicateHint(raw)}`;
+}
+
+/** cpal order is arbitrary; sort by readable label, current OS default first. */
+export function sortAudioDeviceIds(devices: string[], osDefaultDeviceId: string | null): string[] {
+  return [...devices].sort((a, b) => {
+    const aDef = osDefaultDeviceId && a === osDefaultDeviceId;
+    const bDef = osDefaultDeviceId && b === osDefaultDeviceId;
+    if (aDef !== bDef) return aDef ? -1 : 1;
+    const la = formatAudioDeviceLabel(a);
+    const lb = formatAudioDeviceLabel(b);
+    const byLabel = la.localeCompare(lb, undefined, { sensitivity: 'base' });
+    if (byLabel !== 0) return byLabel;
+    return a.localeCompare(b);
+  });
+}
+
+export function buildAudioDeviceSelectOptions(
+  devices: string[],
+  defaultLabel: string,
+  osDefaultDeviceId: string | null,
+  osDefaultMark: string,
+  pinnedDevice: string | null,
+  notInListSuffix: string,
+): { value: string; label: string }[] {
+  const baseLabels = devices.map(formatAudioDeviceLabel);
+  const countByBase = new Map<string, number>();
+  for (const b of baseLabels) countByBase.set(b, (countByBase.get(b) ?? 0) + 1);
+  const pinned = pinnedDevice?.trim() || null;
+  const pinnedNotListed = !!(pinned && !devices.includes(pinned));
+  const ghost: { value: string; label: string }[] = pinnedNotListed
+    ? (() => {
+        const base = formatAudioDeviceLabel(pinned);
+        let label = `${base} · ${notInListSuffix}`;
+        if (osDefaultDeviceId && pinned === osDefaultDeviceId) label = `${label} · ${osDefaultMark}`;
+        return [{ value: pinned, label }];
+      })()
+    : [];
+  return [
+    { value: '', label: defaultLabel },
+    ...ghost,
+    ...devices.map((d, i) => {
+      const base = baseLabels[i];
+      const dup = (countByBase.get(base) ?? 0) > 1;
+      let label = disambiguatedAudioDeviceLabel(d, base, dup);
+      if (osDefaultDeviceId && d === osDefaultDeviceId) label = `${label} · ${osDefaultMark}`;
+      return { value: d, label };
+    }),
+  ];
+}