all: apply golangci-lint autofixes

Go 1.27 allows setting promoted fields of embedded structs directly in
composite literals, so gorm.Model wrappers go away. Plus strings.Cut,
errors.AsType, reflect.TypeAssert and one gofumpt nit.

hscontrol/types/node_tags_test.go

@@ -5,7 +5,6 @@ import (
 
 	"github.com/juanfont/headscale/hscontrol/util"
 	"github.com/stretchr/testify/assert"
-	"gorm.io/gorm"
 )
 
 // TestNodeIsTagged tests the [Node.IsTagged] method for determining if a node is tagged.
@@ -285,7 +284,7 @@ func TestNodeOwnershipModel(t *testing.T) {
 // TestUserTypedID tests the TypedID() helper method.
 func TestUserTypedID(t *testing.T) {
 	user := User{
-		Model: gorm.Model{ID: 42},
+		ID: 42,
 	}
 
 	typedID := user.TypedID()

hscontrol/types/users.go

@@ -40,7 +40,7 @@ const (
 // Tagged nodes don't belong to a real user - the tag is their identity.
 // This special user ID is used when rendering tagged nodes in the Tailscale protocol.
 var TaggedDevices = User{
-	Model:       gorm.Model{ID: TaggedDevicesUserID},
+	ID:          TaggedDevicesUserID,
 	Name:        "tagged-devices",
 	DisplayName: "Tagged Devices",
 }