fix(flutter): cover URLs resolve against server baseUrl + audio stream URL guard

Cover-art Image.network calls were passing server-relative URLs
(/api/albums/<id>/cover) straight to NetworkImage, which interprets
"no scheme" as file:/// and crashes with "No host specified in URI".
Same root cause regardless of HTTPS or HTTP server.

ServerImage wraps Image.network with a Riverpod read of
serverUrlProvider and prefixes the configured base URL. Absolute URLs
(e.g. discover screen's Lidarr image_urls) pass through unchanged.

Three call sites updated: album_card, artist_card, playlists_list_screen.
discover_screen left as-is — its row.imageUrl is already absolute (Lidarr
returns full URLs from MusicBrainz / Spotify metadata) and it has a
meaningful errorBuilder that ServerImage doesn't expose.

Also adds a defensive check in audio_handler.setQueueFromTracks: if
the constructed stream URL ends up scheme-less, throw a StateError
naming baseUrl + track.streamUrl + track.id instead of letting it
fall through to ExoPlayer which surfaces a confusing "Cleartext HTTP
traffic to 127.0.0.1 not permitted" error (Android's URL parser
defaults a scheme-less URI to localhost). User reported this exact
confusing error against an HTTPS prod server; the better message
will pinpoint where the empty baseUrl comes from on next reproduction.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/lib/library/widgets/album_card.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_svg/flutter_svg.dart';
 
 import '../../models/album.dart';
+import '../../shared/widgets/server_image.dart';
 import '../../theme/theme_extension.dart';
 
 class AlbumCard extends StatelessWidget {
@@ -27,7 +28,7 @@ class AlbumCard extends StatelessWidget {
                 color: fs.slate,
                 child: album.coverUrl.isEmpty
                     ? SvgPicture.asset('assets/svg/album-fallback.svg', fit: BoxFit.cover)
-                    : Image.network(album.coverUrl, fit: BoxFit.cover),
+                    : ServerImage(url: album.coverUrl, fit: BoxFit.cover),
               ),
             ),
             const SizedBox(height: 8),

flutter_client/lib/library/widgets/artist_card.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_svg/flutter_svg.dart';
 
 import '../../models/artist.dart';
+import '../../shared/widgets/server_image.dart';
 import '../../theme/theme_extension.dart';
 
 class ArtistCard extends StatelessWidget {
@@ -26,7 +27,7 @@ class ArtistCard extends StatelessWidget {
                 color: fs.slate,
                 child: artist.coverUrl.isEmpty
                     ? SvgPicture.asset('assets/svg/album-fallback.svg', fit: BoxFit.cover)
-                    : Image.network(artist.coverUrl, fit: BoxFit.cover),
+                    : ServerImage(url: artist.coverUrl, fit: BoxFit.cover),
               ),
             ),
             const SizedBox(height: 8),

flutter_client/lib/player/audio_handler.dart

@@ -26,12 +26,21 @@ class MinstrelAudioHandler extends BaseAudioHandler with QueueHandler, SeekHandl
 
     final headers = _token == null ? null : {'Authorization': 'Bearer $_token'};
     final sources = tracks.map((t) {
-      final url = t.streamUrl.isNotEmpty
+      final url = _resolveStreamUrl(t);
-          ? (Uri.tryParse(t.streamUrl)?.hasScheme == true
+      // Defensive: a scheme-less URL handed to ExoPlayer crashes with
-              ? t.streamUrl
+      // a confusing "Cleartext HTTP traffic to 127.0.0.1 not permitted"
-              : '$_baseUrl${t.streamUrl}')
+      // error because Android's URL parser falls back to localhost.
-          : '$_baseUrl/api/tracks/${t.id}/stream';
+      // Surface the actual URL so debugging is straightforward.
-      return AudioSource.uri(Uri.parse(url), headers: headers);
+      final parsed = Uri.parse(url);
+      if (!parsed.hasScheme || parsed.host.isEmpty) {
+        throw StateError(
+          'audio_handler: refused to play scheme-less URL "$url" '
+          '(baseUrl="$_baseUrl", track.streamUrl="${t.streamUrl}", '
+          'track.id="${t.id}"). configure() must be called with a '
+          'non-empty baseUrl before setQueueFromTracks().',
+        );
+      }
+      return AudioSource.uri(parsed, headers: headers);
     }).toList();
 
     await _player.setAudioSources(
@@ -40,6 +49,17 @@ class MinstrelAudioHandler extends BaseAudioHandler with QueueHandler, SeekHandl
     );
   }
 
+  String _resolveStreamUrl(TrackRef t) {
+    if (t.streamUrl.isEmpty) {
+      return '$_baseUrl/api/tracks/${t.id}/stream';
+    }
+    final parsed = Uri.tryParse(t.streamUrl);
+    if (parsed != null && parsed.hasScheme) {
+      return t.streamUrl;
+    }
+    return '$_baseUrl${t.streamUrl}';
+  }
+
   MediaItem _toMediaItem(TrackRef t) => MediaItem(
         id: t.id,
         title: t.title,

flutter_client/lib/playlists/playlists_list_screen.dart

@@ -4,6 +4,7 @@ import 'package:go_router/go_router.dart';
 
 import '../models/playlist.dart';
 import '../shared/widgets/main_app_bar_actions.dart';
+import '../shared/widgets/server_image.dart';
 import '../theme/theme_extension.dart';
 import 'playlists_provider.dart';
 
@@ -81,7 +82,7 @@ class _PlaylistTile extends StatelessWidget {
               color: fs.slate,
               child: playlist.coverUrl.isEmpty
                   ? Icon(Icons.queue_music, color: fs.ash)
-                  : Image.network(playlist.coverUrl, fit: BoxFit.cover),
+                  : ServerImage(url: playlist.coverUrl, fit: BoxFit.cover),
             ),
           ),
           const SizedBox(width: 12),

flutter_client/lib/shared/widgets/server_image.dart

@@ -0,0 +1,47 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../../auth/auth_provider.dart';
+
+/// Image.network wrapper that resolves server-relative URLs (e.g.
+/// `/api/albums/<id>/cover`) against the configured server base URL
+/// from [serverUrlProvider]. Absolute URLs (with scheme) pass through
+/// unchanged. Empty/null base or empty URL render the [fallback]
+/// (defaults to a transparent SizedBox so callers can supply their own
+/// surrounding placeholder).
+///
+/// Mirrors the absolute-or-relative logic the audio handler uses for
+/// stream URLs, so cover art and audio resolve URLs the same way.
+class ServerImage extends ConsumerWidget {
+  const ServerImage({
+    super.key,
+    required this.url,
+    this.fit,
+    this.fallback,
+  });
+
+  final String url;
+  final BoxFit? fit;
+  final Widget? fallback;
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final empty = fallback ?? const SizedBox.shrink();
+    if (url.isEmpty) return empty;
+    final base = ref.watch(serverUrlProvider).value;
+    final resolved = _resolve(base, url);
+    if (resolved == null) return empty;
+    return Image.network(resolved, fit: fit);
+  }
+
+  static String? _resolve(String? baseUrl, String url) {
+    final parsed = Uri.tryParse(url);
+    if (parsed != null && parsed.hasScheme) return url;
+    if (baseUrl == null || baseUrl.isEmpty) return null;
+    final base = baseUrl.endsWith('/')
+        ? baseUrl.substring(0, baseUrl.length - 1)
+        : baseUrl;
+    final path = url.startsWith('/') ? url : '/$url';
+    return '$base$path';
+  }
+}