feat: Enhance companion connection features and UI updates

- Added functionality to load and restore the last companion's scope on app startup.
- Implemented caching mechanisms for contacts, channels, and messages related to the current companion.
- Updated UI to reflect connection status, including disabling message input when disconnected.
- Introduced new dialog prompts to inform users when they need to connect to a companion for accessing features.
- Refactored navigation logic to improve user experience when disconnected, directing users to the scanner screen.
- Added localization strings for new companion connection prompts in multiple languages.

lib/utils/disconnect_navigation_mixin.dart

@@ -1,20 +0,0 @@
-import 'package:flutter/material.dart';
-import '../connector/meshcore_connector.dart';
-
-/// Mixin that automatically navigates back to scanner when disconnected.
-/// Use in State classes for screens that require active connection.
-mixin DisconnectNavigationMixin<T extends StatefulWidget> on State<T> {
-  /// Call this in your Widget build method to enable auto-navigation.
-  /// Returns true if still connected, false if navigation was triggered.
-  bool checkConnectionAndNavigate(MeshCoreConnector connector) {
-    if (!connector.isConnected) {
-      WidgetsBinding.instance.addPostFrameCallback((_) {
-        if (mounted) {
-          Navigator.popUntil(context, (route) => route.isFirst);
-        }
-      });
-      return false;
-    }
-    return true;
-  }
-}