Add accent colour picker, fix empty user card when accepting friend request, add button to transfer allocations

lib/services/theme_mode_service.dart

@@ -0,0 +1,47 @@
+import 'package:flutter/material.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+class ThemeModeService extends ChangeNotifier {
+  static const _prefsKey = 'theme_mode_preference';
+
+  ThemeMode _mode = ThemeMode.system;
+  bool _loaded = false;
+
+  ThemeMode get mode => _mode;
+  bool get isLoaded => _loaded;
+
+  ThemeModeService() {
+    _load();
+  }
+
+  Future<void> _load() async {
+    final prefs = await SharedPreferences.getInstance();
+    final saved = prefs.getString(_prefsKey);
+    if (saved != null) {
+      switch (saved) {
+        case 'light':
+          _mode = ThemeMode.light;
+          break;
+        case 'dark':
+          _mode = ThemeMode.dark;
+          break;
+        default:
+          _mode = ThemeMode.system;
+      }
+    }
+    _loaded = true;
+    notifyListeners();
+  }
+
+  Future<void> setMode(ThemeMode mode) async {
+    _mode = mode;
+    final prefs = await SharedPreferences.getInstance();
+    final value = switch (mode) {
+      ThemeMode.light => 'light',
+      ThemeMode.dark => 'dark',
+      _ => 'system',
+    };
+    await prefs.setString(_prefsKey, value);
+    notifyListeners();
+  }
+}