feat: 统一服务缓存 + 指纹驱动插件匹配

将 webServiceCache 扩展为通用 serviceCache，所有指纹识别结果
统一缓存，插件匹配时端口不命中则回退到服务名称匹配。

删除多余的 service_cache.go，复用已有的 ServiceInfo 体系。
补充 nil 防御、Explicit 标记、大量单元/集成/回归测试。

plugins/local/systeminfo_dc_url.go

@@ -0,0 +1,11 @@
+package local
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+)
+
+func ldapURL(host string, port int) string {
+	return fmt.Sprintf("ldap://%s", net.JoinHostPort(host, strconv.Itoa(port)))
+}

plugins/local/systeminfo_dc_url_test.go

@@ -0,0 +1,24 @@
+package local
+
+import "testing"
+
+func TestLDAPURLUsesJoinHostPort(t *testing.T) {
+	tests := []struct {
+		name string
+		host string
+		port int
+		want string
+	}{
+		{name: "hostname", host: "dc.example.local", port: 389, want: "ldap://dc.example.local:389"},
+		{name: "ipv4", host: "192.168.1.10", port: 389, want: "ldap://192.168.1.10:389"},
+		{name: "ipv6", host: "2001:db8::10", port: 389, want: "ldap://[2001:db8::10]:389"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := ldapURL(tt.host, tt.port); got != tt.want {
+				t.Fatalf("ldapURL(%q, %d) = %q, want %q", tt.host, tt.port, got, tt.want)
+			}
+		})
+	}
+}

plugins/local/systeminfo_dc_windows.go

@@ -82,10 +82,10 @@ func (p *SystemInfoPlugin) connectToDomain(domain string) (*domainInfo, error) {
 	}
 	defer func() { _ = client.Close() }()
 
-	conn, err := ldap.DialURL(fmt.Sprintf("ldap://%s:389", dcHost))
+	conn, err := ldap.DialURL(ldapURL(dcHost, 389))
 	if err != nil {
 		if ipv4, resolveErr := resolveIPv4(dcHost); resolveErr == nil {
-			conn, err = ldap.DialURL(fmt.Sprintf("ldap://%s:389", ipv4))
+			conn, err = ldap.DialURL(ldapURL(ipv4, 389))
 		}
 		if err != nil {
 			return nil, fmt.Errorf("LDAP dial: %w", err)