main: 引入 AgentProvider 流式事件与 OpenAI 兼容适配

- 增加流式事件流支持，Provider 输出 `message.delta` 等事件
- 实现 OpenAI 兼容适配器，包括 RequestBuilder、ApiClient 等模块
- 更新 Agent Run 逻辑，支持流式增量写入与模型完成状态管理
- 扩展配置项 `agent.openai.*`，支持模型、密钥等配置
- 优化文档，完善流式事件与消息类型说明
- 增加单元测试，覆盖 Provider 和 OpenAI 适配相关逻辑
- 更新环境变量与配置示例，支持新功能

tests/Feature/AgentRunTest.php

@@ -4,8 +4,9 @@ namespace Tests\Feature;
 
 use App\Jobs\AgentRunJob;
 use App\Models\Message;
+use App\Services\Agent\AgentContext;
 use App\Services\Agent\AgentProviderInterface;
-use App\Services\Agent\ProviderException;
+use App\Services\Agent\ProviderEvent;
 use App\Services\CancelChecker;
 use App\Services\ChatService;
 use App\Services\RunDispatcher;
@@ -204,14 +205,17 @@ class AgentRunTest extends TestCase
         $this->assertTrue($messages->contains(fn ($m) => $m->type === 'run.status' && ($m->payload['status'] ?? null) === 'CANCELED'));
     }
 
-    public function test_provider_exception_writes_error_and_failed_status(): void
+    public function test_provider_error_event_writes_error_and_failed_status(): void
     {
         Queue::fake();
         $this->app->bind(AgentProviderInterface::class, function () {
             return new class implements AgentProviderInterface {
-                public function generate(array $context, array $options = []): string
+                public function stream(AgentContext $context, array $options = []): \Generator
                 {
-                    throw new ProviderException('HTTP_ERROR', 'provider failed', true, 500, 'boom');
+                    yield ProviderEvent::error('HTTP_ERROR', 'provider failed', [
+                        'retryable' => true,
+                        'http_status' => 500,
+                    ]);
                 }
             };
         });
@@ -229,16 +233,11 @@ class AgentRunTest extends TestCase
 
         $runId = $dispatcher->dispatchForPrompt($session->session_id, $prompt->message_id);
 
-        try {
-            (new AgentRunJob($session->session_id, $runId))->handle(
-                app(RunLoop::class),
-                app(OutputSink::class),
-                app(CancelChecker::class)
-            );
-            $this->fail('Expected provider exception');
-        } catch (ProviderException $exception) {
-            $this->assertSame('HTTP_ERROR', $exception->errorCode);
-        }
+        (new AgentRunJob($session->session_id, $runId))->handle(
+            app(RunLoop::class),
+            app(OutputSink::class),
+            app(CancelChecker::class)
+        );
 
         $messages = Message::query()
             ->where('session_id', $session->session_id)