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/routes/library/[id]/+page.svelte

@@ -84,7 +84,7 @@
 
     try {
       item = await library.loadItem(itemId);
-      console.log(`[LibraryDetail] ✓ Loaded item: ${item?.name} (${item?.type})`);
+      console.log(`[LibraryDetail] ✓ Loaded item: ${item?.name} (${item?.kind})`);
       console.log(`[LibraryDetail] - Has people? ${item?.people ? `YES (${item.people.length})` : 'NO'}`);
       if (item?.people) {
         item.people.forEach((p, i) => {
@@ -170,9 +170,9 @@
 
   // Images now handled by CachedImage component
 
-  function formatDuration(ticks?: number): string {
-    if (!ticks) return "";
-    const seconds = Math.floor(ticks / 10000000);
+  function formatDuration(ms?: number | null): string {
+    if (!ms) return "";
+    const seconds = Math.floor(ms / 1000);
     const hours = Math.floor(seconds / 3600);
     const minutes = Math.floor((seconds % 3600) / 60);
 
@@ -183,7 +183,7 @@
   }
 
   function handleItemClick(clickedItem: MediaItem | Library) {
-    if (!("type" in clickedItem)) {
+    if (!("kind" in clickedItem)) {
       // Library item - navigate to library
       goto(`/library/${clickedItem.id}`);
       return;
@@ -405,8 +405,8 @@
             {#if item.type}
               <span class="px-2 py-1 bg-[var(--color-surface)] rounded">{item.type}</span>
             {/if}
-            {#if item.runTimeTicks}
-              <span>{formatDuration(item.runTimeTicks)}</span>
+            {#if item.durationMs}
+              <span>{formatDuration(item.durationMs)}</span>
             {/if}
             {#if item.communityRating}
               <span class="flex items-center gap-1">