fix(flutter): silence 404 log noise from missing playlist covers

Playlist collages aren't generated until the build job runs over a
playlist with tracks — system playlists (For-You / Discover / Songs-
like) and any newly-created playlist hit a brief window where
/api/playlists/:id/cover returns 404. ServerImage's errorWidget
already renders the visual fallback (queue_music icon over slate);
this fix just keeps cached_network_image from spamming the dev
console with HttpExceptionWithStatus stack traces.

errorListener filters 404 specifically — auth (401/403) and any
5xx still log so real connectivity / permission issues stay visible.

User-visible behavior unchanged; this is a dev-mode log hygiene fix.

flutter_client/lib/shared/widgets/server_image.dart

@@ -1,5 +1,8 @@
 import 'package:cached_network_image/cached_network_image.dart';
+import 'package:flutter/foundation.dart' show debugPrint;
 import 'package:flutter/material.dart';
+import 'package:flutter_cache_manager/flutter_cache_manager.dart'
+    show HttpExceptionWithStatus;
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../../auth/auth_provider.dart';
@@ -71,6 +74,19 @@ class ServerImage extends ConsumerWidget {
           // Keep failures local — a single 401/timeout shouldn't dump
           // a stack trace or replace the parent Container's background.
           errorWidget: (_, __, ___) => empty,
+          // Filter expected 404s out of dev console noise: playlist
+          // collages aren't built until the playlist has tracks and
+          // the build job runs (system playlists like For-You /
+          // Discover hit this on first-render). The errorWidget
+          // already renders the fallback for the user; this just
+          // keeps the dev console clean. Non-404 errors still
+          // surface so auth/connectivity issues remain visible.
+          errorListener: (err) {
+            if (err is HttpExceptionWithStatus && err.statusCode == 404) {
+              return;
+            }
+            debugPrint('ServerImage: $err');
+          },
         );
       },
     );