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。

libs/grdp/login/screen_test.go

@@ -0,0 +1,24 @@
+package login
+
+import "testing"
+
+func TestRDPTargetHost(t *testing.T) {
+	tests := []struct {
+		name   string
+		target string
+		want   string
+	}{
+		{name: "ipv4 with port", target: "192.168.1.1:3389", want: "192.168.1.1"},
+		{name: "hostname with port", target: "rdp.example.com:3389", want: "rdp.example.com"},
+		{name: "bracketed ipv6 with port", target: "[2001:db8::1]:3389", want: "2001:db8::1"},
+		{name: "bare ipv6 without port", target: "2001:db8::1", want: "2001:db8::1"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := rdpTargetHost(tt.target); got != tt.want {
+				t.Fatalf("rdpTargetHost(%q) = %q, want %q", tt.target, got, tt.want)
+			}
+		})
+	}
+}