refactor(ui): use shared loading indicators

lib/screens/artist_screen.dart

@@ -5,6 +5,7 @@ import 'package:flutter/cupertino.dart';
 import 'package:spotiflac_android/theme/mornye_theme.dart';
 import 'package:spotiflac_android/widgets/app_alert_dialog.dart';
 import 'package:spotiflac_android/widgets/app_icon_button.dart';
+import 'package:spotiflac_android/widgets/app_loading_indicator.dart';
 import 'package:spotiflac_android/widgets/app_progress_indicator.dart';
 import 'package:spotiflac_android/widgets/expressive_button.dart';
 import 'package:spotiflac_android/theme/mornye_icons.dart';
@@ -776,7 +777,7 @@ class _ArtistScreenState extends ConsumerState<ArtistScreen>
                                 textAlign: TextAlign.center,
                               ),
                             if (_isLoadingMoreAlbums)
-                              const CircularProgressIndicator.adaptive(),
+                              const AppLoadingIndicator(),
                           ],
                         ),
                       ),

lib/screens/settings/extension_detail_page.dart

@@ -1077,7 +1077,7 @@ class _SettingItemState extends State<_SettingItem> {
           trailing = const SizedBox(
             width: 24,
             height: 24,
-            child: CircularProgressIndicator.adaptive(strokeWidth: 2),
+            child: AppLoadingIndicator(size: 24, strokeWidth: 2),
           );
         }
         break;

lib/widgets/library_search_results.dart

@@ -23,6 +23,7 @@ import 'package:spotiflac_android/widgets/library_selection_playback_actions.dar
 import 'package:spotiflac_android/widgets/selection_bottom_bar.dart';
 import 'package:spotiflac_android/widgets/track_card.dart';
 import 'package:spotiflac_android/widgets/app_icon_button.dart';
+import 'package:spotiflac_android/widgets/app_loading_indicator.dart';
 import 'package:spotiflac_android/widgets/expressive_button.dart';
 
 /// Slivers shared by Material's Library and Mornye's Library/Songs screens.
@@ -462,7 +463,7 @@ class _LibrarySearchResultsState extends ConsumerState<LibrarySearchResults> {
         const SliverToBoxAdapter(
           child: Padding(
             padding: EdgeInsets.all(24),
-            child: Center(child: CircularProgressIndicator.adaptive()),
+            child: Center(child: AppLoadingIndicator()),
           ),
         ),
       );