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

app/Services/Agent/OpenAi/OpenAiStreamParser.php

@@ -0,0 +1,75 @@
+<?php
+
+namespace App\Services\Agent\OpenAi;
+
+use Psr\Http\Message\StreamInterface;
+
+class OpenAiStreamParser
+{
+    public function __construct(private readonly int $chunkSize = 1024)
+    {
+    }
+
+    /**
+     * Parses SSE data lines into payload strings.
+     *
+     * @return \Generator<int, string>
+     */
+    public function parse(StreamInterface $stream, ?callable $shouldStop = null): \Generator
+    {
+        $buffer = '';
+        $eventData = '';
+
+        while (! $stream->eof()) {
+            if ($shouldStop && $shouldStop()) {
+                break;
+            }
+
+            $chunk = $stream->read($this->chunkSize);
+
+            if ($chunk === '') {
+                usleep(10000);
+                continue;
+            }
+
+            $buffer .= $chunk;
+
+            while (($pos = strpos($buffer, "\n")) !== false) {
+                $line = substr($buffer, 0, $pos);
+                $buffer = substr($buffer, $pos + 1);
+                $line = rtrim($line, "\r");
+
+                if ($line === '') {
+                    if ($eventData !== '') {
+                        yield $eventData;
+                        $eventData = '';
+                    }
+                    continue;
+                }
+
+                if (str_starts_with($line, 'data:')) {
+                    $data = ltrim(substr($line, 5));
+                    if ($eventData !== '') {
+                        $eventData .= "\n";
+                    }
+                    $eventData .= $data;
+                }
+            }
+        }
+
+        if ($buffer !== '') {
+            $line = rtrim($buffer, "\r");
+            if (str_starts_with($line, 'data:')) {
+                $data = ltrim(substr($line, 5));
+                if ($eventData !== '') {
+                    $eventData .= "\n";
+                }
+                $eventData .= $data;
+            }
+        }
+
+        if ($eventData !== '') {
+            yield $eventData;
+        }
+    }
+}