improved performance and battery usage on older devices

lib/view/pages/settings/chat_background_settings_page.dart

@@ -214,8 +214,11 @@ class ChatBackgroundSettingsPage extends StatelessWidget {
       final file = File(AppPaths.chatBackgroundImage);
       await file.writeAsBytes(bytes);
       // Same filename across replacements → the decoded image is cached under
-      // an identical key. Evict so the new bytes actually show.
-      await FileImage(file).evict();
+      // an identical key (for "cover" also wrapped in a viewport-sized
+      // ResizeImage). Clearing the cache is fine for this rare action.
+      PaintingBinding.instance.imageCache
+        ..clear()
+        ..clearLiveImages();
       final cs = settings.val(write: true).chatBackgroundSettings;
       cs.imageVersion++;
       cs.type = ChatBackgroundType.image;

lib/view/pages/settings/sections/dev_tools_section.dart

@@ -3,13 +3,13 @@ import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:hydrated_bloc/hydrated_bloc.dart';
 
+import '../../../../api/cache_store.dart';
 import '../../../../routing/app_routes.dart';
 import '../../../../state/app/modules/settings/bloc/settings_cubit.dart';
 import '../../../../storage/dev_tools_settings.dart';
 import '../../../../storage/settings.dart' as model;
 import '../../../../widget/centered_leading.dart';
 import '../../../../widget/confirm_dialog.dart';
-import '../../../../widget/debug/cache_view.dart';
 import '../../../../widget/debug/json_viewer.dart';
 import '../../../../widget/details_bottom_sheet.dart';
 import '../widgets/endpoint_picker.dart';
@@ -24,6 +24,9 @@ class DevToolsSection extends StatefulWidget {
 }
 
 class _DevToolsSectionState extends State<DevToolsSection> {
+  // Kept across rebuilds: the size walk lists the whole cache directory.
+  Future<int>? _cacheSize;
+
   @override
   Widget build(BuildContext context) => Column(
     children: [
@@ -153,7 +156,7 @@ class _DevToolsSectionState extends State<DevToolsSection> {
         leading: const CenteredLeading(Icon(Icons.data_object)),
         title: const Text('Cache-storage JSON dump'),
         subtitle: FutureBuilder(
-          future: const CacheView().totalSize(),
+          future: _cacheSize ??= CacheStore.instance.totalSize(),
           builder: (context, snapshot) => Text(
             "etwa ${snapshot.hasError
                 ? "?"
@@ -169,8 +172,9 @@ class _DevToolsSectionState extends State<DevToolsSection> {
             content:
                 'Alle cache Einträge werden gelöscht. Der Cache wird bei Nutzung der App automatisch erneut aufgebaut',
             confirmButton: 'Unwiederruflich löschen',
-            onConfirm: () =>
-                const CacheView().clear().then((value) => setState(() {})),
+            onConfirm: () => CacheStore.instance.clear().then(
+              (value) => setState(() => _cacheSize = null),
+            ),
           ).asDialog(context);
         },
         trailing: const Icon(Icons.arrow_right),