feat(orbit): sync the host's track-transition settings to guests (#1158)

* feat(orbit): mirror host track-transition settings into the session

Each client previously used its own local crossfade / gapless / AutoDJ
settings, so guests blended tracks differently from the host and drifted
out of sync — the exact drift the Catch-Up button exists to paper over.

Add an optional OrbitSettings.transitions (crossfade enabled/secs/trim,
AutoDJ smooth-skip, gapless), additive on the wire so older sessions
simply omit it. The host seeds its own prefs at start and refreshes them
every tick, so a mid-session change propagates. Guests snapshot their own
prefs on join, adopt the host's for the session (idempotent — no setState
churn / audio-sync re-fire when unchanged), and restore their own on
leave. Applying via authStore.setState reuses the existing authSyncListener
path to the Rust engine, so no new IPC. Without the Hot cache a guest's
AutoDJ blend degrades gracefully via the existing byte-preload fallback.

Add a bridge module with unit tests for read/apply/save/restore.

* feat(orbit): lock guest transition controls during a session

Since a guest now mirrors the host's track-transition settings (re-applied
every read tick), their own controls would visibly fight the sync. Disable
them while a guest is in a live session and explain why.

Settings -> Audio -> Track transitions greys out the mode picker, seconds
slider and smooth-skip toggle with a "controlled by the Orbit host" note;
the queue toolbar's Gapless / Crossfade / AutoDJ quick-toggles get the same
disabled state and tooltip. Host controls are untouched. New i18n key added
across all locales.

* docs(changelog): add Orbit transition sync (1158)

src/utils/orbit.ts

@@ -46,6 +46,12 @@ export {
   writeOrbitHeartbeat,
   writeOrbitState,
 } from './orbit/remote';
+export {
+  readOrbitTransitionSettings,
+  applyOrbitTransitionSettings,
+  saveGuestTransitionsOnce,
+  restoreGuestTransitions,
+} from './orbit/transitions';
 export {
   buildOrbitShareLink,
   parseOrbitShareLink,