fix: Size the gallery fallback icon frame to fill the thumbnail box (#2705)

- Closes: #2701

tests/browser/fake-frigate.ts

@@ -226,6 +226,7 @@ const matchesEventQuery = (event: FrigateEvent, query: EventQuery): boolean =>
 export class FakeFrigate {
   private _events: FrigateEvent[] = [];
   private _mediaURLs = new Map<string, string>();
+  private _thumbnailFailureStatus: number | null = null;
 
   constructor(hass: FakeHASS) {
     hass.registerCommand(
@@ -306,6 +307,13 @@ export class FakeFrigate {
     this._mediaURLs.set(this._getMediaKey(eventID, mediaType), url);
   }
 
+  /**
+   * Refuse every thumbnail request with the given HTTP status.
+   */
+  public failThumbnails(status = 404): void {
+    this._thumbnailFailureStatus = status;
+  }
+
   // Answer a command addressed to this instance, refusing one meant for
   // another. Frigate answers with JSON.
   private _answerAsFrigate(
@@ -397,6 +405,10 @@ export class FakeFrigate {
       throw new Error(`FakeFrigate has no thumbnail at: ${path}`);
     }
 
+    if (this._thumbnailFailureStatus !== null) {
+      return new Response(null, { status: this._thumbnailFailureStatus });
+    }
+
     return await fetch(createFixtureURL(SNAPSHOT_FIXTURE_FILENAME));
   }
 }