feat: persist token_version in config, auto-detect on load

- NetBoxConfig.TokenVersion saved to netssh.yaml by the wizard
- config.Load() auto-detects the version from the token prefix if the
  field is missing (backwards-compatible with existing configs)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/setup/wizard.go

@@ -103,7 +103,8 @@ func RunWizard(cfg *config.Config) error {
 		return err
 	}
 
-	if netbox.TokenVersion(token) == 1 {
+	tokenVersion := netbox.TokenVersion(token)
+	if tokenVersion == 1 {
 		fmt.Fprintln(os.Stderr, "\nHinweis: Du verwendest einen Legacy-Token (v1). Erstelle in NetBox einen v2-Token (beginnt mit nbt_) für bessere Kompatibilität.")
 		fmt.Fprintln(os.Stderr, "  NetBox → Admin → API Tokens → Add Token")
 	}
@@ -119,8 +120,9 @@ func RunWizard(cfg *config.Config) error {
 
 	out := config.Config{
 		NetBox: config.NetBoxConfig{
-			URL:   strings.TrimRight(strings.TrimSpace(url), "/"),
-			Token: strings.TrimSpace(token),
+			URL:          strings.TrimRight(strings.TrimSpace(url), "/"),
+			Token:        strings.TrimSpace(token),
+			TokenVersion: tokenVersion,
 		},
 		SSH: config.SSHConfig{
 			DefaultUser: strings.TrimSpace(defaultUser),
@@ -148,6 +150,7 @@ func save(cfg config.Config) error {
 	b.WriteString("netbox:\n")
 	b.WriteString(fmt.Sprintf("  url: %q\n", cfg.NetBox.URL))
 	b.WriteString(fmt.Sprintf("  token: %q\n", cfg.NetBox.Token))
+	fmt.Fprintf(&b, "  token_version: %d\n", cfg.NetBox.TokenVersion)
 
 	b.WriteString("\nresolver:\n")
 	b.WriteString("  strategies:\n")