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/locales/de/settings.ts

@@ -170,6 +170,11 @@ export const settings = {
   showTrayIconDesc: 'Psysonic-Icon im System-Tray / in der Menüleiste anzeigen.',
   minimizeToTray: 'Im Tray minimieren',
   minimizeToTrayDesc: 'Beim Schließen des Fensters läuft Psysonic weiter im System-Tray statt zu beenden.',
+  clockFormat: 'Uhrzeitformat',
+  clockFormatDesc: 'Format für die Queue-ETA und die Vorschau des Sleep-Timers.',
+  clockFormatAuto: 'Automatisch (Systemsprache)',
+  clockFormatTwentyFour: '24-Stunden',
+  clockFormatTwelve: '12-Stunden (AM/PM)',
   preloadMiniPlayer: 'Mini-Player vorladen',
   preloadMiniPlayerDesc: 'Baut das Mini-Player-Fenster beim App-Start im Hintergrund auf, damit es beim ersten Öffnen sofort Inhalt zeigt. Kostet etwas mehr RAM.',
   discordRichPresence: 'Discord Rich Presence',