feat(dns): 优化系统工具箱DNS设置以适配现代Linux系统 (#1202)

* Initial plan

* feat(dns): 优化系统工具箱DNS设置以适配现代Linux系统

- 创建 pkg/dns 包实现多种DNS管理方式
- 支持 NetworkManager (RHEL 9.x/10.x)
- 支持 netplan (Debian 12+/Ubuntu 22+)
- 回退到直接修改 /etc/resolv.conf
- 更新前端显示当前DNS管理方式
- 添加单元测试

Co-authored-by: devhaozi <115467771+devhaozi@users.noreply.github.com>

* fix: 修复代码审查发现的问题

- 提取 shell 参数转义逻辑到独立函数
- 修正 netplan 配置文件选择的注释说明
- 使用常量替代硬编码的缩进值
- 添加前端空数组安全检查

Co-authored-by: devhaozi <115467771+devhaozi@users.noreply.github.com>

* fix: 优化

* fix: 优化

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: devhaozi <115467771+devhaozi@users.noreply.github.com>
Co-authored-by: 耗子 <haozi@loli.email>

internal/service/toolbox_system.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/acepanel/panel/internal/app"
 	"github.com/acepanel/panel/internal/http/request"
+	"github.com/acepanel/panel/pkg/dns"
 	"github.com/acepanel/panel/pkg/io"
 	"github.com/acepanel/panel/pkg/ntp"
 	"github.com/acepanel/panel/pkg/shell"
@@ -32,19 +33,16 @@ func NewToolboxSystemService(t *gotext.Locale) *ToolboxSystemService {
 
 // GetDNS 获取 DNS 信息
 func (s *ToolboxSystemService) GetDNS(w http.ResponseWriter, r *http.Request) {
-	raw, err := io.Read("/etc/resolv.conf")
+	dnsServers, manager, err := dns.GetDNS()
 	if err != nil {
 		Error(w, http.StatusInternalServerError, "%v", err)
 		return
 	}
 
-	match := regexp.MustCompile(`nameserver\s+(\S+)`).FindAllStringSubmatch(raw, -1)
-	dns := make([]string, 0)
-	for _, m := range match {
-		dns = append(dns, m[1])
-	}
-
-	Success(w, dns)
+	Success(w, chix.M{
+		"dns":     dnsServers,
+		"manager": manager.String(),
+	})
 }
 
 // UpdateDNS 设置 DNS 信息
@@ -55,11 +53,7 @@ func (s *ToolboxSystemService) UpdateDNS(w http.ResponseWriter, r *http.Request)
 		return
 	}
 
-	var dns string
-	dns += "nameserver " + req.DNS1 + "\n"
-	dns += "nameserver " + req.DNS2 + "\n"
-
-	if err := io.Write("/etc/resolv.conf", dns, 0644); err != nil {
+	if err := dns.SetDNS(req.DNS1, req.DNS2); err != nil {
 		Error(w, http.StatusInternalServerError, s.t.Get("failed to update DNS: %v", err))
 		return
 	}