Speed up large movement gallery entry (Byzantine)

Hall frames use thumbs only (never multi-MB originals). Preload no longer blocks open; texture downloads are queued; boot overlay no longer waits on HDR Environment.

Co-authored-by: Cursor <cursoragent@cursor.com>

client/src/api/client.ts

@@ -177,7 +177,7 @@ export function galleryImageUrl(
   return null;
 }
 
-/** Ordered texture URL candidates for a hall frame (thumb → full → on-demand API). */
+/** Ordered hall texture URLs — thumbs only (never full originals; those can be 10MB+ each). */
 export function galleryImageUrlCandidates(
   painting: {
     id?: number;
@@ -194,10 +194,14 @@ export function galleryImageUrlCandidates(
     if (u && !urls.includes(u)) urls.push(u);
   };
   if (painting.thumbnail_path) push(imageUrl(painting.thumbnail_path, revision));
-  if (painting.image_path) push(imageUrl(painting.image_path, revision));
+  // If DB has no thumb path but has a full file, still prefer the on-demand thumb API
+  // over streaming the multi-megabyte original into WebGL.
   if (painting.id != null) {
     push(`/api/paintings/${painting.id}/image?size=thumb`);
   }
+  if (!painting.thumbnail_path && painting.image_path) {
+    push(imageUrl(painting.image_path, revision));
+  }
   return urls;
 }