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/screens/chat_screen.dart

@@ -414,7 +414,7 @@ class _ChatScreenState extends State<ChatScreen> {
                   ],
                 ),
               ),
-              _buildInputBar(connector),
+              if (connector.isConnected) _buildInputBar(connector),
             ],
           );
         },
@@ -693,6 +693,9 @@ class _ChatScreenState extends State<ChatScreen> {
   }
 
   Future<void> _sendMessage(MeshCoreConnector connector) async {
+    if (!connector.isConnected) {
+      return;
+    }
     final text = _textController.text.trim();
     if (text.isEmpty) return;