feat: 支持Anthropic API协议 | support Anthropic API protocol

- 添加Anthropic适配器实现 | Add Anthropic adaptor implementation
- 支持Anthropic消息格式转换 | Support Anthropic message format conversion
- 添加Vertex AI Claude适配器支持 | Add Vertex AI Claude adapter support
- 更新Anthropic的中继模式定义 | Update relay mode definitions for Anthropic
- 添加Anthropic控制器和路由 | Add Anthropic controller and routing

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: zgdmemail@gmail.com

relay/relaymode/define.go

@@ -13,4 +13,6 @@ const (
 	AudioTranslation
 	// Proxy is a special relay mode for proxying requests to custom upstream
 	Proxy
+	// AnthropicMessages is for native Anthropic API messages endpoint
+	AnthropicMessages
 )

relay/relaymode/helper.go

@@ -26,6 +26,8 @@ func GetByPath(path string) int {
 		relayMode = AudioTranslation
 	} else if strings.HasPrefix(path, "/v1/oneapi/proxy") {
 		relayMode = Proxy
+	} else if strings.HasPrefix(path, "/anthropic/v1/messages") {
+		relayMode = AnthropicMessages
 	}
 	return relayMode
 }