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/macos/Flutter/GeneratedPluginRegistrant.swift

@@ -0,0 +1,16 @@
+//
+//  Generated file. Do not edit.
+//
+
+import FlutterMacOS
+import Foundation
+
+import flutter_appauth
+import flutter_secure_storage_macos
+import path_provider_foundation
+
+func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
+  FlutterAppauthPlugin.register(with: registry.registrar(forPlugin: "FlutterAppauthPlugin"))
+  FlutterSecureStoragePlugin.register(with: registry.registrar(forPlugin: "FlutterSecureStoragePlugin"))
+  PathProviderPlugin.register(with: registry.registrar(forPlugin: "PathProviderPlugin"))
+}