Version: 0.9.65.dev.260503

后端：
1. 阶段 1.5/1.6
收口 llm-service / rag-service，统一模型出口与检索基础设施入口，清退 backend/infra/llm 与 backend/infra/rag 旧实现；
2. 同步更新相关调用链与微服务迁移计划文档

backend/services/llm/ark.go

@@ -0,0 +1,73 @@
+package llm
+
+import (
+	"context"
+	"errors"
+	"strings"
+
+	"github.com/cloudwego/eino-ext/components/model/ark"
+	einoModel "github.com/cloudwego/eino/components/model"
+	"github.com/cloudwego/eino/schema"
+	arkModel "github.com/volcengine/volcengine-go-sdk/service/arkruntime/model"
+)
+
+// ArkCallOptions 是直接调用 ark.ChatModel 时使用的通用入参。
+type ArkCallOptions struct {
+	Temperature float64
+	MaxTokens   int
+	Thinking    ThinkingMode
+}
+
+// CallArkText 调用 ark 模型并返回纯文本。
+func CallArkText(ctx context.Context, chatModel *ark.ChatModel, systemPrompt, userPrompt string, options ArkCallOptions) (string, error) {
+	if chatModel == nil {
+		return "", errors.New("ark model is nil")
+	}
+
+	messages := []*schema.Message{
+		schema.SystemMessage(systemPrompt),
+		schema.UserMessage(userPrompt),
+	}
+	resp, err := chatModel.Generate(ctx, messages, buildArkOptions(options)...)
+	if err != nil {
+		return "", err
+	}
+	if resp == nil {
+		return "", errors.New("模型返回为空")
+	}
+
+	text := strings.TrimSpace(resp.Content)
+	if text == "" {
+		return "", errors.New("模型返回内容为空")
+	}
+	return text, nil
+}
+
+// CallArkJSON 调用 ark 模型并直接解析 JSON。
+func CallArkJSON[T any](ctx context.Context, chatModel *ark.ChatModel, systemPrompt, userPrompt string, options ArkCallOptions) (*T, string, error) {
+	raw, err := CallArkText(ctx, chatModel, systemPrompt, userPrompt, options)
+	if err != nil {
+		return nil, "", err
+	}
+	parsed, err := ParseJSONObject[T](raw)
+	if err != nil {
+		return nil, raw, err
+	}
+	return parsed, raw, nil
+}
+
+func buildArkOptions(options ArkCallOptions) []einoModel.Option {
+	thinkingType := arkModel.ThinkingTypeDisabled
+	if options.Thinking == ThinkingModeEnabled {
+		thinkingType = arkModel.ThinkingTypeEnabled
+	}
+
+	opts := []einoModel.Option{
+		ark.WithThinking(&arkModel.Thinking{Type: thinkingType}),
+		einoModel.WithTemperature(float32(options.Temperature)),
+	}
+	if options.MaxTokens > 0 {
+		opts = append(opts, einoModel.WithMaxTokens(options.MaxTokens))
+	}
+	return opts
+}