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/config/settingsCredits.ts

@@ -297,6 +297,7 @@ const CONTRIBUTOR_ENTRIES = [
       'Song Info: absolute file path on Navidrome via native /api/song/{id} — Subsonic only ever returned a relative path (or none on Navidrome), the native endpoint surfaces the full server-side location (PR #504)',
       'Home: Lossless Albums rail + dedicated /lossless-albums page with infinite scroll and header parity (selection mode, enqueue, offline, download ZIPs), streaming load via per-fetch onProgress, sidebar entry default visible, detection via Navidrome native bit_depth-sorted song cursor with always-lossless suffix allowlist (PR #506)',
       'Accessibility: OpenDyslexic font option in the Settings picker — bundled locally via @fontsource/opendyslexic, asymmetric glyph shapes for easier b/d, p/q tracking, Latin-only with translated subtitle in all 9 locales calling out the dyslexia-friendly intent and the Cyrillic/CJK fallback (PR #507)',
+      'Settings: tri-state Clock Format (Auto / 24h / 12h) overriding the locale default for the queue ETA and the sleep-timer preview (PR #742)',
     ],
   },
 ] as const;