feat: embed a Flutter G4F client with Cronet, cookie jar, and origin WebView

Port the Oracle off the Python g4f container onto on-device providers: Chromium HTTP via Cronet, a shared cookie session, IterList retry, hosted OpenAI-compat aggregators, and same-origin WebView fallbacks instead of CORS fetch.

windows/flutter/generated_plugin_registrant.cc

@@ -6,6 +6,9 @@
 
 #include "generated_plugin_registrant.h"
 
+#include <flutter_inappwebview_windows/flutter_inappwebview_windows_plugin_c_api.h>
 
 void RegisterPlugins(flutter::PluginRegistry* registry) {
+  FlutterInappwebviewWindowsPluginCApiRegisterWithRegistrar(
+      registry->GetRegistrarForPlugin("FlutterInappwebviewWindowsPluginCApi"));
 }