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/lib/stores/movies.ts

@@ -45,7 +45,7 @@ function createMoviesStore() {
 
   /** Artwork check for hero candidates: needs a backdrop or a primary image. */
   const hasArt = (i: MediaItem) =>
-    !!(i.backdropImageTags && i.backdropImageTags.length > 0) || !!i.primaryImageTag;
+    !!(i.backdropImageTags && i.backdropImageTags.length > 0) || !!i.imageId;
 
   async function loadSections(libraryId: string) {
     update(s => ({

src/lib/stores/music.ts

@@ -55,7 +55,7 @@ function createMusicStore() {
 
   /** Artwork check for hero candidates: needs a primary image or backdrop. */
   const hasArt = (i: MediaItem) =>
-    !!i.primaryImageTag || !!(i.backdropImageTags && i.backdropImageTags.length > 0);
+    !!i.imageId || !!(i.backdropImageTags && i.backdropImageTags.length > 0);
 
   async function loadSections(libraryId: string) {
     update(s => ({

src/lib/stores/player.ts

@@ -9,7 +9,7 @@
  */
 
 import { writable, derived } from "svelte/store";
-import type { MediaItem, ItemType } from "$lib/api/types";
+import type { MediaItem, MediaKind } from "$lib/api/types";
 import type { NowPlayingItem } from "$lib/api/bindings";
 import { isRemoteMode } from "./playbackMode";
 import { selectedSession } from "./sessions";
@@ -24,7 +24,7 @@ export interface MergedMediaItem {
   album: string | null;
   albumId: string | null;
   duration: number | null;
-  primaryImageTag: string | null;
+  imageId: string | null;
   mediaType: "audio" | "video";
 }
 
@@ -170,16 +170,24 @@ export const isMuted = derived(player, ($p) => $p.muted);
  * falls back to the `artists` string list when `artistItems` is absent.)
  */
 function nowPlayingToMediaItem(npi: NowPlayingItem): MediaItem {
+  // NowPlayingItem is remote-session data still carrying Jellyfin field names
+  // (Type, runTimeTicks, primaryImageTag). Map it onto the neutral MediaItem the
+  // UI consumes. Only the coarse audio/video split matters here for display.
+  const kind: MediaKind =
+    npi.Type === "Movie" ? "movie" :
+    npi.Type === "Episode" ? "episode" :
+    npi.Type === "MusicAlbum" ? "album" :
+    "track";
   return {
     id: npi.id ?? "",
     name: npi.name ?? "",
-    type: (npi.Type ?? "Audio") as ItemType,
+    kind,
     serverId: "",
     albumName: npi.album,
     albumId: npi.albumId,
     artists: npi.artists,
-    primaryImageTag: npi.primaryImageTag ?? npi.albumPrimaryImageTag,
-    runTimeTicks: npi.runTimeTicks,
+    imageId: npi.primaryImageTag ?? npi.albumPrimaryImageTag,
+    durationMs: npi.runTimeTicks != null ? Math.floor(npi.runTimeTicks / 10000) : null,
   } as MediaItem;
 }
 

src/lib/stores/tv.ts

@@ -50,7 +50,7 @@ function createTvStore() {
   const hasArt = (i: MediaItem) =>
     !!(i.backdropImageTags && i.backdropImageTags.length > 0) ||
     !!(i.parentBackdropImageTags && i.parentBackdropImageTags.length > 0) ||
-    !!i.primaryImageTag;
+    !!i.imageId;
 
   async function loadSections(libraryId: string) {
     update(s => ({