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,
   )