feat(mobile): Implement Keycloak WebView authentication with HTTP callback

- Replace flutter_appauth with custom WebView implementation to resolve deep link issues
- Add KeycloakWebViewAuthService with integrated WebView for seamless authentication
- Configure Android manifest for HTTP cleartext traffic support
- Add network security config for development environment (192.168.1.11)
- Update Keycloak client to use HTTP callback endpoint (http://192.168.1.11:8080/auth/callback)
- Remove obsolete keycloak_auth_service.dart and temporary scripts
- Clean up dependencies and regenerate injection configuration
- Tested successfully on multiple Android devices (Xiaomi 2201116TG, SM A725F)

BREAKING CHANGE: Authentication flow now uses WebView instead of external browser
- Users will see Keycloak login page within the app instead of browser redirect
- Resolves ERR_CLEARTEXT_NOT_PERMITTED and deep link state management issues
- Maintains full OIDC compliance with PKCE flow and secure token storage

Technical improvements:
- WebView with custom navigation delegate for callback handling
- Automatic token extraction and user info parsing from JWT
- Proper error handling and user feedback
- Consistent authentication state management across app lifecycle

keycloak_test_app/linux/my_application.h

@@ -0,0 +1,18 @@
+#ifndef FLUTTER_MY_APPLICATION_H_
+#define FLUTTER_MY_APPLICATION_H_
+
+#include <gtk/gtk.h>
+
+G_DECLARE_FINAL_TYPE(MyApplication, my_application, MY, APPLICATION,
+                     GtkApplication)
+
+/**
+ * my_application_new:
+ *
+ * Creates a new Flutter-based application.
+ *
+ * Returns: a new #MyApplication.
+ */
+MyApplication* my_application_new();
+
+#endif  // FLUTTER_MY_APPLICATION_H_