fix(cli): handle inline PEM CA content in artifact download

The artifact download command unconditionally passed the CAS CA config
value to WithCAFile(), which fails with "file name too long" when the
value contains inline PEM content instead of a file path. Use os.Stat()
to distinguish paths from PEM content, matching the existing pattern in
root.go and action.go.

Signed-off-by: Javier Rodriguez <javier@chainloop.dev>

Author: javirln

app/cli/cmd/artifact.go

@@ -1,5 +1,5 @@
 //
-// Copyright 2023-2025 The Chainloop Authors.
+// Copyright 2023-2026 The Chainloop Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@ package cmd
 
 import (
 	"context"
+	"os"
 
 	pb "github.com/chainloop-dev/chainloop/app/controlplane/api/controlplane/v1"
 	"github.com/chainloop-dev/chainloop/pkg/grpcconn"
@@ -54,8 +55,12 @@ func wrappedArtifactConn(cpConn *grpc.ClientConn, role pb.CASCredentialsServiceG
 		grpcconn.WithInsecure(apiInsecure()),
 	}
 
-	if caFilePath := viper.GetString(confOptions.CASCA.viperKey); caFilePath != "" {
-		opts = append(opts, grpcconn.WithCAFile(caFilePath))
+	if caValue := viper.GetString(confOptions.CASCA.viperKey); caValue != "" {
+		if _, err := os.Stat(caValue); err == nil {
+			opts = append(opts, grpcconn.WithCAFile(caValue))
+		} else {
+			opts = append(opts, grpcconn.WithCAContent(caValue))
+		}
 	}
 
 	return grpcconn.New(viper.GetString(confOptions.CASAPI.viperKey), resp.Result.Token, opts...)