Fix 'secret get' to output to stdout instead of stderr

- Add Print method to CLI Instance that uses cmd.OutOrStdout()
- Update GetSecretWithVersion to use cli.Print instead of cmd.Print
- Add test to verify secret values go to stdout, not stderr
- Store command reference in Instance for proper output handling

internal/cli/cli.go

@@ -2,6 +2,8 @@
 package cli
 
 import (
+	"fmt"
+
 	"git.eeqj.de/sneak/secret/internal/secret"
 	"github.com/spf13/afero"
 	"github.com/spf13/cobra"
@@ -57,3 +59,8 @@ func (cli *Instance) SetStateDir(stateDir string) {
 func (cli *Instance) GetStateDir() string {
 	return cli.stateDir
 }
+
+// Print outputs to the command's configured output writer
+func (cli *Instance) Print(a ...interface{}) (n int, err error) {
+	return fmt.Fprint(cli.cmd.OutOrStdout(), a...)
+}