fix: list-routes command now respects identifier filter with JSON output

Fixes #2927

In v0.27.0, the list-routes command with -i flag and -o json output
was returning all nodes instead of just the specified node.

The issue was that JSON output was happening before the identifier
filtering logic. This change moves the JSON output to after both
the identifier filter and route existence filter are applied,
ensuring the correct filtered results are returned.

This restores the v0.26.1 behavior where:
  headscale nodes list-routes -i 12 -o json
correctly returns only node 12's route information.

cmd/headscale/cli/nodes.go

@@ -220,10 +220,6 @@ var listNodeRoutesCmd = &cobra.Command{
 			)
 		}
 
-		if output != "" {
-			SuccessOutput(response.GetNodes(), "", output)
-		}
-
 		nodes := response.GetNodes()
 		if identifier != 0 {
 			for _, node := range response.GetNodes() {
@@ -238,6 +234,11 @@ var listNodeRoutesCmd = &cobra.Command{
 			return (n.GetSubnetRoutes() != nil && len(n.GetSubnetRoutes()) > 0) || (n.GetApprovedRoutes() != nil && len(n.GetApprovedRoutes()) > 0) || (n.GetAvailableRoutes() != nil && len(n.GetAvailableRoutes()) > 0)
 		})
 
+		if output != "" {
+			SuccessOutput(nodes, "", output)
+			return
+		}
+
 		tableData, err := nodeRoutesToPtables(nodes)
 		if err != nil {
 			ErrorOutput(err, fmt.Sprintf("Error converting to table: %s", err), output)