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/store/authStore.settings.test.ts

@@ -54,6 +54,7 @@ describe('trivial pass-through setters', () => {
     ['setShowArtistImages', 'showArtistImages', true],
     ['setShowTrayIcon', 'showTrayIcon', false],
     ['setMinimizeToTray', 'minimizeToTray', true],
+    ['setClockFormat', 'clockFormat', '24h'],
     ['setShowOrbitTrigger', 'showOrbitTrigger', false],
     ['setDiscordRichPresence', 'discordRichPresence', true],
     ['setEnableBandsintown', 'enableBandsintown', true],