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/commands/player/queue.rs

@@ -211,6 +211,7 @@ pub async fn player_add_track_by_id(
         artist_items: track.artist_items.clone(), // For clickable artist links
         artists: track.artists.clone(),           // Fallback artist info
         primary_image_tag: track.primary_image_tag.clone(), // For frontend image display
+        image_id: track.primary_image_tag.clone(),
         item_type: Some(track.item_type.clone()), // Frontend compatibility
         playlist_id: None,
         duration: track.runtime_ticks.map(|t| t as f64 / 10_000_000.0),
@@ -329,6 +330,7 @@ pub async fn player_add_tracks_by_ids(
             artist_items: track.artist_items.clone(), // For clickable artist links
             artists: track.artists.clone(),           // Fallback artist info
             primary_image_tag: track.primary_image_tag.clone(), // For frontend image display
+            image_id: track.primary_image_tag.clone(),
             item_type: Some(track.item_type.clone()), // Frontend compatibility
             playlist_id: None,
             duration: track.runtime_ticks.map(|t| t as f64 / 10_000_000.0),