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/repository/offline.rs

@@ -128,8 +128,7 @@ impl OfflineRepository {
                 let playback_position_ticks: Option<i64> = row.get(0).ok();
                 Ok(UserData {
                     playback_position_ticks,
-                    playback_position_ms: playback_position_ticks
-                        .map(crate::domain::ticks_to_ms),
+                    playback_position_ms: playback_position_ticks.map(crate::domain::ticks_to_ms),
                     is_played: row.get::<_, Option<i32>>(1).ok().flatten().map(|v| v != 0),
                     is_favorite: row.get::<_, Option<i32>>(2).ok().flatten().map(|v| v != 0),
                     play_count: row.get(3).ok(),