fix(ui): fall back to the default avatar when a profile image fails to load (#28270)

src/lib/components/chat/Messages/ProfileImage.svelte

@@ -6,7 +6,9 @@
 	// LICENSE covers this Open WebUI fallback logo.
 	// Do not alter, remove, obscure, or replace it except as LICENSE permits:
 	// https://docs.openwebui.com/license.
-	export let src = `${WEBUI_BASE_URL}/static/favicon.png`;
+	const FALLBACK_SRC = `${WEBUI_BASE_URL}/static/favicon.png`;
+
+	export let src = FALLBACK_SRC;
 </script>
 
 <img
@@ -15,4 +17,9 @@
 	class=" {className} object-cover rounded-2xl"
 	alt="profile"
 	draggable="false"
+	on:error={(e) => {
+		if (!e.currentTarget.src.endsWith(FALLBACK_SRC)) {
+			e.currentTarget.src = FALLBACK_SRC;
+		}
+	}}
 />