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/components/player/AudioPlayer.svelte

@@ -143,7 +143,7 @@
         <CachedImage
           itemId={artworkItemId}
           imageType="Primary"
-          tag={displayMedia?.primaryImageTag}
+          tag={displayMedia?.imageId}
           maxWidth={800}
           alt=""
           class="w-full h-full object-cover blur-3xl opacity-30"
@@ -223,7 +223,7 @@
           <CachedImage
             itemId={artworkItemId}
             imageType="Primary"
-            tag={displayMedia?.primaryImageTag}
+            tag={displayMedia?.imageId}
             maxWidth={500}
             alt={displayMedia?.name}
             class="w-full h-full object-cover"

src/lib/components/player/MiniPlayer.svelte

@@ -326,7 +326,7 @@
             <CachedImage
               itemId={displayMedia.albumId || displayMedia.id}
               imageType="Primary"
-              tag={displayMedia.primaryImageTag}
+              tag={displayMedia.imageId}
               maxWidth={100}
               alt={displayMedia?.name}
               class="w-full h-full object-cover"

src/lib/components/player/NextEpisodePopup.svelte

@@ -78,11 +78,11 @@
         <div
           class="relative flex-shrink-0 w-28 h-16 rounded-lg overflow-hidden bg-gray-800"
         >
-          {#if imageId && $nextEpisodeItem.primaryImageTag}
+          {#if imageId && $nextEpisodeItem.imageId}
             <CachedImage
               itemId={imageId}
               imageType="Primary"
-              tag={$nextEpisodeItem.primaryImageTag}
+              tag={$nextEpisodeItem.imageId}
               maxHeight={200}
               alt={$nextEpisodeItem.name}
               class="w-full h-full object-cover"

src/lib/components/player/Queue.svelte

@@ -184,11 +184,11 @@
 
                 <!-- Artwork -->
                 <div class="w-10 h-10 rounded bg-gray-800 flex-shrink-0 overflow-hidden">
-                  {#if item.primaryImageTag}
+                  {#if item.imageId}
                     <CachedImage
                       itemId={item.id}
                       imageType="Primary"
-                      tag={item.primaryImageTag}
+                      tag={item.imageId}
                       maxWidth={80}
                       alt={item.name}
                       class="w-full h-full object-cover"

src/lib/components/player/VideoPlayer.svelte

@@ -1223,7 +1223,7 @@
           needsTranscoding: false,
           // Now-playing metadata so the lockscreen/miniplayer show the item.
           artist: media.seriesName ?? null,
-          primaryImageTag: media.primaryImageTag ?? null,
+          primaryImageTag: media.imageId ?? null,
           serverId: media.serverId ?? null,
           // Real duration so the lockscreen scrubber has a range to draw.
           durationSeconds: duration > 0 ? duration : null,
@@ -1626,11 +1626,11 @@
     {#if !isMediaReady}
       <div class="absolute inset-0 flex items-center justify-center bg-black">
         <!-- Poster/Title Card -->
-        {#if media?.primaryImageTag}
+        {#if media?.imageId}
           <CachedImage
             itemId={media.id}
             imageType="Primary"
-            tag={media.primaryImageTag}
+            tag={media.imageId}
             maxHeight={1080}
             alt={media?.name || "Video"}
             class="max-w-full max-h-full object-contain"