refactor: 重构目录结构，后端代码统一到 backend/ 目录

backend/internal/llm/chatmodel.go

@@ -0,0 +1,76 @@
+package llm
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"ai-agent-scaffold-go/internal/model"
+)
+
+// ChatModelAdapter 适配器，将 OpenAIClient 包装为 model.ChatModel
+type ChatModelAdapter struct {
+	client *OpenAIClient
+	tools  []model.Tool
+}
+
+// NewChatModelAdapter 创建 ChatModel 适配器
+func NewChatModelAdapter(client *OpenAIClient, tools []model.Tool) *ChatModelAdapter {
+	return &ChatModelAdapter{client: client, tools: tools}
+}
+
+// Generate 实现 model.ChatModel 接口
+func (m *ChatModelAdapter) Generate(ctx context.Context, messages []model.ChatMessage) (model.ChatReply, error) {
+	return m.client.Generate(ctx, messages, m.toolDefs())
+}
+
+// Stream 实现 model.ChatModel 接口
+func (m *ChatModelAdapter) Stream(ctx context.Context, messages []model.ChatMessage) (<-chan model.ChatStreamEvent, <-chan error) {
+	return m.client.Stream(ctx, messages, m.toolDefs())
+}
+
+// Tools 返回注册的工具列表
+func (m *ChatModelAdapter) Tools() []model.Tool {
+	return m.tools
+}
+
+// CallTool 根据名称和参数调用对应的工具
+func (m *ChatModelAdapter) CallTool(ctx context.Context, name, arguments string) (string, error) {
+	query := extractQuery(arguments)
+	for _, t := range m.tools {
+		if t.Name() == name {
+			return t.Call(ctx, query)
+		}
+	}
+	return "", fmt.Errorf("tool %q not found", name)
+}
+
+// toolDefs 将 model.Tool 转换为 ToolDef 列表
+func (m *ChatModelAdapter) toolDefs() []ToolDef {
+	defs := make([]ToolDef, 0, len(m.tools))
+	for _, t := range m.tools {
+		defs = append(defs, ToolDef{Name: t.Name(), Description: t.Description()})
+	}
+	return defs
+}
+
+// extractQuery 从工具调用参数 JSON 中提取 query 字段
+func extractQuery(arguments string) string {
+	arguments = strings.TrimSpace(arguments)
+	if arguments == "" {
+		return ""
+	}
+	if idx := strings.Index(arguments, `"query"`); idx >= 0 {
+		rest := arguments[idx+7:]
+		if colon := strings.Index(rest, `:`); colon >= 0 {
+			rest = strings.TrimSpace(rest[colon+1:])
+			if strings.HasPrefix(rest, `"`) {
+				rest = rest[1:]
+				if end := strings.Index(rest, `"`); end >= 0 {
+					return rest[:end]
+				}
+			}
+		}
+	}
+	return arguments
+}