domain: flip isVideoItem in player store to .kind (phase 2a completion)

The catalog MediaItem check in stores/player.ts isVideoItem() was missed
in the phase 2a sweep (excluded by a player-path filter). It reads the
catalog MediaItem, so it flips like the rest: type Movie/Episode/TvChannel
-> kind movie/episode/liveChannel.

Verified: no catalog .type === "<JellyfinType>" comparisons remain in the
frontend (only stream.type in VideoPlayer, deferred to phase 4). check clean.

src/lib/stores/player.ts

@@ -263,8 +263,8 @@ export const mergedVolume = derived(
  */
 function isVideoItem(item: MediaItem | null): boolean {
   if (!item) return false;
-  const type = item.type;
-  if (type === "Movie" || type === "Episode" || type === "TvChannel") {
+  const kind = item.kind;
+  if (kind === "movie" || kind === "episode" || kind === "liveChannel") {
     return true;
   }
   // Backend PlayerMediaItem carries a lowercase mediaType discriminator that is