Cover art thumbnails

library scan creates thumbnails, cover grid component defaults to
thumbnail if available.

frontend/src/components/cover-grid/cover-grid.ts

@@ -278,9 +278,15 @@ export class CoverGrid extends LitElement {
                     ${album.CoverArtPath
                         ? html`<img
                               class="cover-image"
-                              src="${album.CoverArtPath}"
+                              src="${album.CoverArtThumbnailPath || album.CoverArtPath}"
                               alt="${album.Name} cover"
                               loading="lazy"
+                              @error=${(e: Event) => {
+                                  const img = e.target as HTMLImageElement;
+                                  if (img.src !== album.CoverArtPath) {
+                                      img.src = album.CoverArtPath;
+                                  }
+                              }}
                           />`
                         : html`<div class="placeholder-cover">
                               ${this.getAlbumInitial(album.Name)}

frontend/src/components/now-playing/now-playing.ts

@@ -85,7 +85,16 @@ export class NowPlaying extends LitElement {
       <div class="now-playing">
         <div class="cover-art">
           ${track.coverArt
-            ? html`<img src="${track.coverArt}" alt="Album cover" />`
+            ? html`<img
+                src="${track.coverArtThumbnail || track.coverArt}"
+                alt="Album cover"
+                @error=${(e: Event) => {
+                    const img = e.target as HTMLImageElement;
+                    if (track.coverArt && img.src !== track.coverArt) {
+                        img.src = track.coverArt;
+                    }
+                }}
+              />`
             : html`<div class="cover-placeholder"><wa-icon name="music"></wa-icon></div>`}
         </div>
         <div class="track-info">

frontend/src/store/player-store.ts

@@ -12,6 +12,7 @@ export interface TrackInfo {
   artist: string; // artist name
   album: string; // album name
   coverArt: string; // URL path to cover art (e.g., "/covers/abc.jpg") or empty string
+  coverArtThumbnail: string; // URL path to thumbnail (e.g., "/covers/abc_thumb.jpg") or empty string
 }
 
 export interface PlayerState {