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/lib/components/library/LibraryListView.svelte

@@ -42,10 +42,10 @@
 
 
   function getProgress(item: MediaItem | Library): number {
-    if (!showProgress || !("userData" in item) || !item.userData || !("runTimeTicks" in item) || !item.runTimeTicks) {
+    if (!showProgress || !("userData" in item) || !item.userData || !("durationMs" in item) || !item.durationMs) {
       return 0;
     }
-    return ((item.userData.playbackPositionTicks ?? 0) / item.runTimeTicks) * 100;
+    return ((item.userData.playbackPositionMs ?? 0) / item.durationMs) * 100;
   }
 
   function getTrackNumber(item: MediaItem | Library): string {
@@ -59,7 +59,7 @@
 <div class="space-y-1">
   {#each items as item, index (item.id)}
     {@const subtitle = getSubtitle(item)}
-    {@const duration = "runTimeTicks" in item ? formatDuration(item.runTimeTicks) : ""}
+    {@const duration = "durationMs" in item ? formatDuration(item.durationMs) : ""}
     {@const progress = getProgress(item)}
     {@const trackNum = getTrackNumber(item)}
     {@const isPlayed = "userData" in item && item.userData?.isPlayed}