Implement chat server auth, models, handlers, and docs context

lib/config/config.dart

@@ -1,12 +1,12 @@
 class Config {
   // Server settings
   static const int port = 9870;
-  
+
   // IMPORTANT: Set this to your actual server host/domain
   // Used for generating userId: "username@serverHost"
   static const String serverHost = 'localhost:9870';
   static const String serverName = 'Chat Server';
-  
+
   // JWT settings
   // TODO: Move to environment variable in production
   static const String jwtSecret = 'your_super_secret_key_change_in_production';