feat: 添加邮件服务器客户端库的基础功能

- 新增完整的Go客户端库实现，支持邮件服务器API的各种操作
- 实现账户管理、签名管理、邮件发送、审计、配额、通道等功能模块
- 提供ServiceAuth和AppAuth两种认证模式的客户端
- 添加详细的README文档，包含安装指南和使用示例
- 配置.gitignore文件以忽略构建产物和开发工具配置
- 支持分页查询、错误处理和客户端选项配置

audit.go

@@ -0,0 +1,54 @@
+package emailcli
+
+import (
+	"context"
+	"fmt"
+)
+
+func (c *Client) ListAuditPending(ctx context.Context, q AuditPendingQuery) (*PaginationResult[MailLog], error) {
+	params := mergeParams(paginationParams(q.PaginationQuery), map[string]interface{}{
+		"user_id":    q.UserID,
+		"account_id": q.AccountID,
+		"keyword":    q.Keyword,
+	})
+	return get[*PaginationResult[MailLog]](c, ctx, "/api/v1/audits/pending", buildQuery(params))
+}
+
+func (c *Client) GetAuditPendingDetail(ctx context.Context, id uint) (*MailLogDetail, error) {
+	return get[*MailLogDetail](c, ctx, fmt.Sprintf("/api/v1/audits/pending/%d", id), nil)
+}
+
+func (c *Client) ApproveAudit(ctx context.Context, id uint) error {
+	_, err := post[any](c, ctx, fmt.Sprintf("/api/v1/audits/%d/approve", id), nil)
+	return err
+}
+
+func (c *Client) RejectAudit(ctx context.Context, id uint, req AuditRejectReq) error {
+	_, err := post[any](c, ctx, fmt.Sprintf("/api/v1/audits/%d/reject", id), req)
+	return err
+}
+
+func (c *Client) BatchApproveAudit(ctx context.Context, req BatchAuditApproveReq) error {
+	_, err := post[any](c, ctx, "/api/v1/audits/batch/approve", req)
+	return err
+}
+
+func (c *Client) BatchRejectAudit(ctx context.Context, req BatchAuditRejectReq) error {
+	_, err := post[any](c, ctx, "/api/v1/audits/batch/reject", req)
+	return err
+}
+
+func (c *Client) ListAuditLogs(ctx context.Context, q AuditLogQuery) (*PaginationResult[MailAudit], error) {
+	params := mergeParams(paginationParams(q.PaginationQuery), map[string]interface{}{
+		"audit_type": q.AuditType,
+		"action":     q.Action,
+		"user_id":    q.UserID,
+		"start_date": q.StartDate,
+		"end_date":   q.EndDate,
+	})
+	return get[*PaginationResult[MailAudit]](c, ctx, "/api/v1/audits/logs", buildQuery(params))
+}
+
+func (c *Client) GetAuditStats(ctx context.Context) (*AuditStats, error) {
+	return get[*AuditStats](c, ctx, "/api/v1/audits/stats", nil)
+}