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

client-simple.json

@@ -0,0 +1,17 @@
+{
+  "clientId": "unionflow-mobile",
+  "name": "UnionFlow Mobile App",
+  "enabled": true,
+  "publicClient": true,
+  "standardFlowEnabled": true,
+  "implicitFlowEnabled": false,
+  "directAccessGrantsEnabled": false,
+  "serviceAccountsEnabled": false,
+  "redirectUris": [
+    "com.unionflow.mobile://login-callback"
+  ],
+  "webOrigins": ["+"],
+  "attributes": {
+    "pkce.code.challenge.method": "S256"
+  }
+}