fix(node-player): load cover art via axios with Bearer token

Cover images were loaded via <img src> which doesn't include the
Authorization header, resulting in 401 from the Rust API. Now covers
are fetched through axios as blobs and displayed via object URLs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

furumi-node-player/client/src/furumiApi.ts

@@ -52,3 +52,9 @@ export async function preloadStream(trackSlug: string) {
   return await furumiApi.get(`/stream/${trackSlug}`, { responseType: 'blob' }).catch(() => null)
 }
 
+export async function fetchCoverBlob(trackSlug: string): Promise<string | null> {
+  const res = await furumiApi.get(`/tracks/${trackSlug}/cover`, { responseType: 'blob' }).catch(() => null)
+  if (!res?.data) return null
+  return URL.createObjectURL(res.data)
+}
+