feat(ux): unify added-to-queue snackbars and add fetch retry

Every single-track enqueue now shows the shared added-to-queue
snackbar with a View action into Library (six call sites through one
helper). URL fetch failures in Home and via share intent gain a Retry
action; unrecognized-URL errors deliberately keep none since retrying
is deterministic.

lib/screens/artist_screen.dart

@@ -1638,12 +1638,7 @@ class _ArtistScreenState extends ConsumerState<ArtistScreen>
       ref
           .read(downloadQueueProvider.notifier)
           .addToQueue(track, service, qualityOverride: quality);
-      ScaffoldMessenger.of(context).showSnackBar(
-        SnackBar(
-          content: Text(context.l10n.snackbarAddedToQueue(track.name)),
-          duration: const Duration(seconds: 2),
-        ),
-      );
+      showAddedToQueueSnackBar(context, track.name);
     }
 
     if (settings.askQualityBeforeDownload || settings.allowQualityVariants) {

lib/screens/home_tab.dart

@@ -543,9 +543,18 @@ class _HomeTabState extends ConsumerState<HomeTab>
             : isRateLimit
             ? l10n.errorRateLimitedMessage
             : l10n.errorUrlFetchFailed;
-        ScaffoldMessenger.of(
-          context,
-        ).showSnackBar(SnackBar(content: Text(displayMessage)));
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(
+            content: Text(displayMessage),
+            // Retrying an unrecognized URL is deterministic; skip the action.
+            action: errorMsg == 'url_not_recognized'
+                ? null
+                : SnackBarAction(
+                    label: l10n.dialogRetry,
+                    onPressed: _fetchMetadata,
+                  ),
+          ),
+        );
         ref.read(trackProvider.notifier).clear();
       } else {
         _navigateToDetailIfNeeded();
@@ -649,11 +658,7 @@ class _HomeTabState extends ConsumerState<HomeTab>
             ref
                 .read(downloadQueueProvider.notifier)
                 .addToQueue(track, service, qualityOverride: quality);
-            ScaffoldMessenger.of(context).showSnackBar(
-              SnackBar(
-                content: Text(context.l10n.snackbarAddedToQueue(track.name)),
-              ),
-            );
+            showAddedToQueueSnackBar(context, track.name);
           },
         );
       } else {
@@ -669,11 +674,7 @@ class _HomeTabState extends ConsumerState<HomeTab>
           return;
         }
         ref.read(downloadQueueProvider.notifier).addToQueue(track, service);
-        ScaffoldMessenger.of(context).showSnackBar(
-          SnackBar(
-            content: Text(context.l10n.snackbarAddedToQueue(track.name)),
-          ),
-        );
+        showAddedToQueueSnackBar(context, track.name);
       }
     }
   }
@@ -1982,11 +1983,7 @@ class _HomeTabState extends ConsumerState<HomeTab>
           ref
               .read(downloadQueueProvider.notifier)
               .addToQueue(track, service, qualityOverride: quality);
-          ScaffoldMessenger.of(context).showSnackBar(
-            SnackBar(
-              content: Text(context.l10n.snackbarAddedToQueue(track.name)),
-            ),
-          );
+          showAddedToQueueSnackBar(context, track.name);
         },
       );
     } else {
@@ -2002,9 +1999,7 @@ class _HomeTabState extends ConsumerState<HomeTab>
         return;
       }
       ref.read(downloadQueueProvider.notifier).addToQueue(track, service);
-      ScaffoldMessenger.of(context).showSnackBar(
-        SnackBar(content: Text(context.l10n.snackbarAddedToQueue(track.name))),
-      );
+      showAddedToQueueSnackBar(context, track.name);
     }
   }
 

lib/screens/main_shell.dart

@@ -300,9 +300,18 @@ class _MainShellState extends ConsumerState<MainShell>
           : isRateLimit
           ? l10n.errorRateLimitedMessage
           : l10n.errorUrlFetchFailed;
-      ScaffoldMessenger.of(
-        context,
-      ).showSnackBar(SnackBar(content: Text(displayMessage)));
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(
+          content: Text(displayMessage),
+          // Retrying an unrecognized URL is deterministic; skip the action.
+          action: errorMsg == 'url_not_recognized'
+              ? null
+              : SnackBarAction(
+                  label: l10n.dialogRetry,
+                  onPressed: () => _handleSharedUrl(url),
+                ),
+        ),
+      );
     }
   }
 

lib/widgets/track_detail_actions.dart

@@ -8,6 +8,7 @@ import 'package:spotiflac_android/providers/library_collections_provider.dart';
 import 'package:spotiflac_android/providers/local_library_provider.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
 import 'package:spotiflac_android/widgets/download_service_picker.dart';
+import 'package:spotiflac_android/widgets/view_queue_snackbar_action.dart';
 
 /// Shared single-track "add to queue" flow for detail screens: shows the
 /// quality/service picker when the user opted into it, otherwise resolves
@@ -24,10 +25,7 @@ void downloadSingleTrack(
   final settings = ref.read(settingsProvider);
 
   void notifyQueued() {
-    if (!context.mounted) return;
-    ScaffoldMessenger.of(context).showSnackBar(
-      SnackBar(content: Text(context.l10n.snackbarAddedToQueue(track.name))),
-    );
+    showAddedToQueueSnackBar(context, track.name);
   }
 
   if (settings.askQualityBeforeDownload || forceQualityPicker) {

lib/widgets/view_queue_snackbar_action.dart

@@ -10,3 +10,14 @@ SnackBarAction buildViewQueueSnackBarAction(BuildContext context) {
     },
   );
 }
+
+/// Shared "Added to queue" snackbar with a View action jumping to Library.
+void showAddedToQueueSnackBar(BuildContext context, String trackName) {
+  if (!context.mounted) return;
+  ScaffoldMessenger.of(context).showSnackBar(
+    SnackBar(
+      content: Text(context.l10n.snackbarAddedToQueue(trackName)),
+      action: buildViewQueueSnackBarAction(context),
+    ),
+  );
+}