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/meta/relay_meta.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/songquanpeng/one-api/common/ctxkey"
 	"github.com/songquanpeng/one-api/model"
+	"github.com/songquanpeng/one-api/relay/apitype"
 	"github.com/songquanpeng/one-api/relay/channeltype"
 	"github.com/songquanpeng/one-api/relay/relaymode"
 )
@@ -62,5 +63,11 @@ func GetByContext(c *gin.Context) *Meta {
 		meta.BaseURL = channeltype.ChannelBaseURLs[meta.ChannelType]
 	}
 	meta.APIType = channeltype.ToAPIType(meta.ChannelType)
+
+	// Force Anthropic API type for native Anthropic protocol requests
+	if meta.Mode == relaymode.AnthropicMessages {
+		meta.APIType = apitype.Anthropic
+	}
+
 	return &meta
 }