feat(settings): clock format setting (Auto / 24h / 12h) (#742)

* feat(settings): clock format setting (Auto / 24h / 12h)

Reported on the Psysonic Discord — the Queue side panel's ETA label
and the sleep-timer preview both render via `formatClockTime`, which
just calls `toLocaleTimeString` and so follows the user's system
locale. On en-US that means AM/PM, with no in-app way out.

Add a tri-state **Clock Format** setting under
**Settings → System → App Behavior**:

* `auto` (default) — keep the existing locale-driven behaviour, so
  bestehende installs are unaffected on first launch.
* `24h` — force 24-hour wall-clock output everywhere
  `formatClockTime` is used.
* `12h` — force AM/PM output.

Wired through `authStore` (`clockFormat`, `setClockFormat`), exposed
via `CustomSelect` in `SystemTab`, and threaded into the two
consumers (`QueueHeader`, `PlaybackDelayModal`) so they re-render on
change. `formatClockTime` itself stays a pure helper — it accepts the
setting as an optional second argument and maps it to `hour12`.

Locale coverage: all nine bundled locales (en, de, es, fr, nl, nb,
ru, zh, ro) get the four new settings strings. Pin tests added for
the `setClockFormat` setter and the `hour12` mapping in
`formatClockTime`.

* docs(changelog): clock format setting + contributors (PR #742)

src/utils/format/formatClockTime.ts

@@ -1,4 +1,15 @@
-/** Localized wall-clock `HH:MM` for a timestamp (sleep-timer / queue-ETA labels). */
-export function formatClockTime(timestampMs: number): string {
-  return new Date(timestampMs).toLocaleTimeString(undefined, { hour: '2-digit', minute: '2-digit' });
+import type { ClockFormat } from '../../store/authStoreTypes';
+
+/**
+ * Localized wall-clock `HH:MM` for a timestamp (sleep-timer / queue-ETA labels).
+ * `clockFormat` overrides the system locale's `hour12` default — pass `'auto'`
+ * or omit to keep locale-driven behaviour.
+ */
+export function formatClockTime(timestampMs: number, clockFormat?: ClockFormat): string {
+  const hour12 = clockFormat === '24h' ? false : clockFormat === '12h' ? true : undefined;
+  return new Date(timestampMs).toLocaleTimeString(undefined, {
+    hour: '2-digit',
+    minute: '2-digit',
+    hour12,
+  });
 }