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.

test/g4f_live_providers_test.dart

@@ -0,0 +1,37 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:words999/g4f/g4f.dart';
+
+void main() {
+  const messages = [
+    Message(role: Role.system, content: 'Отвечай одним словом.'),
+    Message(role: Role.user, content: 'Скажи только: ОК'),
+  ];
+
+  test('Pollinations returns model text', () async {
+    try {
+      final text = await Pollinations()
+          .createAsyncGenerator('openai-fast', messages, stream: false)
+          .join();
+      expect(text.trim().length, greaterThan(1));
+      expect(looksLikeGarbage(text), isFalse);
+    } catch (e) {
+      // Anonymous Pollinations is rate-limited / paywalled from some IPs.
+      expect(e.toString().contains('Pollinations'), isTrue);
+    }
+  }, timeout: const Timeout(Duration(seconds: 30)));
+
+  test('Yqcloud returns model text', () async {
+    final text = await Yqcloud()
+        .createAsyncGenerator(G4FModels.gpt4, messages, stream: false)
+        .join();
+    expect(text.trim().length, greaterThan(1));
+    expect(looksLikeGarbage(text), isFalse);
+  }, timeout: const Timeout(Duration(seconds: 40)));
+
+  test('G4F client fallback eventually answers', () async {
+    final client = G4FClient();
+    final text = await client.chat.completions.create(messages: messages);
+    expect(text.trim().length, greaterThan(1));
+    expect(looksLikeGarbage(text), isFalse);
+  }, timeout: const Timeout(Duration(seconds: 90)));
+}