domain: primaryImageTag -> imageId end-to-end (phase 4a/4b)

Rust: PlayerMediaItem and MergedMediaItem gain image_id (dual-carry),
populated from primary_image_tag at every construction/conversion site.
Regenerated bindings.

Frontend: all catalog + player + merged readers now use imageId. The
NowPlayingItem->MediaItem bridge (player.ts) properly maps the remote
session's Jellyfin fields (Type, runTimeTicks, primaryImageTag) onto the
neutral kind/durationMs/imageId. Types that are genuinely out of scope
(Person, NowPlayingItem, PlayItemRequest) keep primaryImageTag.

Rust 456, frontend 644, check clean.

src-tauri/src/domain/from_jellyfin.rs

@@ -119,7 +119,10 @@ mod tests {
 
     #[test]
     fn channel_and_container_types_map() {
-        assert_eq!(kind_from_jellyfin("TvChannel", false), MediaKind::LiveChannel);
+        assert_eq!(
+            kind_from_jellyfin("TvChannel", false),
+            MediaKind::LiveChannel
+        );
         assert_eq!(kind_from_jellyfin("Channel", false), MediaKind::Channel);
         assert_eq!(
             kind_from_jellyfin("CollectionFolder", true),