domain: catalog frontend off Jellyfin ticks -> milliseconds (phase 3a)

The catalog surface now speaks milliseconds, the app's neutral time unit.
Ticks no longer reach library/home components.

Rust:
- UserData gains playback_position_ms (dual-carry), populated from ticks
  at the offline mapping seam via domain::ticks_to_ms.

Frontend:
- formatDuration(duration.ts) and the two local copies now take ms, not
  ticks; all callers pass item.durationMs.
- Progress bars (EpisodeRow, EpisodeFocusView, MediaCard, LibraryListView)
  compute playbackPositionMs / durationMs — unit-consistent, no tick math.
- PlaylistDetailView totalDuration sums durationMs.
- duration.test.ts + TrackList.test.ts fixtures updated to ms.

Deferred: player/session/reporting tick math (Queue, SessionCard,
RemoteControls, playbackReporting, playerEvents) — those cross the
storage/Jellyfin command boundary in ticks and need command-signature
changes (phase 3b). Display {item.type} badge -> kind label (phase 4).

Rust 456, frontend 644, check + check:boundary clean.

src-tauri/src/repository/offline.rs

@@ -125,8 +125,11 @@ impl OfflineRepository {
 
         self.db_service
             .query_optional(query, |row| {
+                let playback_position_ticks: Option<i64> = row.get(0).ok();
                 Ok(UserData {
-                    playback_position_ticks: row.get(0).ok(),
+                    playback_position_ticks,
+                    playback_position_ms: playback_position_ticks
+                        .map(crate::domain::ticks_to_ms),
                     is_played: row.get::<_, Option<i32>>(1).ok().flatten().map(|v| v != 0),
                     is_favorite: row.get::<_, Option<i32>>(2).ok().flatten().map(|v| v != 0),
                     play_count: row.get(3).ok(),