feat(queue): add Timeline display mode (#1004)

* feat(queue): add Timeline display mode

A third queue display mode alongside Queue and Playlist. Timeline shows
the full queue anchored on the current track — played history above
(dimmed), upcoming below — with 'History' and 'Up next' dividers and the
current row auto-centered. It already follows shuffle order since the
queue is stored in play order. The header mode button now cycles
queue → timeline → playlist; Settings gains a third option.

* i18n(queue): Timeline mode strings (9 locales)

* docs(changelog): note Timeline queue mode (#1004)

src/store/authStoreRehydrate.ts

@@ -106,7 +106,7 @@ export function computeAuthStoreRehydration(state: AuthState): Partial<AuthState
 
   // Missing key (pre-feature persist) / garbage maps to 'queue' — the default
   // mode, which lists only upcoming tracks.
-  const VALID_QUEUE_DISPLAY_MODES = new Set<string>(['playlist', 'queue']);
+  const VALID_QUEUE_DISPLAY_MODES = new Set<string>(['playlist', 'queue', 'timeline']);
   const queueDisplayModeMigrated = VALID_QUEUE_DISPLAY_MODES.has(
     (state as { queueDisplayMode?: unknown }).queueDisplayMode as string,
   )

src/store/authStoreTypes.ts

@@ -42,7 +42,7 @@ export type DurationMode = 'total' | 'remaining' | 'eta';
  * - `queue`: the list shows upcoming tracks only — the current track lives in
  *   the header and drops out of the list once it has played.
  */
-export type QueueDisplayMode = 'playlist' | 'queue';
+export type QueueDisplayMode = 'playlist' | 'queue' | 'timeline';
 export type LoggingMode = 'off' | 'normal' | 'debug';
 /**
  * Wall-clock format for ETA / sleep-timer labels. `'auto'` follows the user's
@@ -185,7 +185,9 @@ export interface AuthState {
   queueNowPlayingCollapsed: boolean;
   /** Queue header duration chip mode (cycle: total → remaining → ETA). */
   queueDurationDisplayMode: DurationMode;
-  /** Queue panel render mode: full timeline (`playlist`) vs. upcoming-only (`queue`). */
+  /** Queue panel render mode: full list from top (`playlist`), upcoming-only
+   *  (`queue`), or full list centered on the current track with history above
+   *  and up-next below (`timeline`). */
   queueDisplayMode: QueueDisplayMode;
 
   /** Alpha: native hi-res sample rate output (disabled = safe 44.1 kHz mode) */