Fix Windows: remove -- separator (psmux incompatible), add unknown command error

- Remove -- separator from tmux args (psmux on Windows doesn't support it)
- Unknown subcommands now show error + usage (exit 1) instead of starting TUI
- --help now always shows usage and exits (no fallthrough to TUI)

cmd/kctl-tui/full.go

@@ -282,16 +282,16 @@ func (m *fullModel) startTmuxSession() tea.Cmd {
 
 	args := []string{
 		"new-session", "-d", "-s", "kctl",
-		"--", panelCmd, ";",
+		panelCmd, ";",
 		"set-option", "-t", "kctl", "remain-on-exit", "on", ";",
-		"split-window", "-v", "-t", "kctl:0.0", "--", k9sCmdA, ";",
+		"split-window", "-v", "-t", "kctl:0.0", k9sCmdA, ";",
 	}
 	if len(m.cfg.Envs) > 1 {
 		envB := m.cfg.Envs[1]
 		ctxB := m.cfg.ResolveContext(envB, m.selectedContext)
 		k9sCmdB := fmt.Sprintf("k9s --context %s -n %s", ctxB, m.selectedNamespace)
 		args = append(args,
-			"split-window", "-v", "-t", "kctl:0.1", "--", k9sCmdB, ";",
+			"split-window", "-v", "-t", "kctl:0.1", k9sCmdB, ";",
 		)
 	}
 	args = append(args,

cmd/kctl-tui/main.go

@@ -39,9 +39,7 @@ func main() {
 
 	if showHelp || len(filtered) == 0 {
 		printUsage()
-		if showHelp && len(filtered) == 0 {
-			return
-		}
+		return
 	}
 
 	if len(filtered) > 0 {
@@ -64,6 +62,10 @@ func main() {
 				os.Exit(1)
 			}
 			return
+		default:
+			fmt.Fprintf(os.Stderr, "unknown command: %s\n\n", filtered[0])
+			printUsage()
+			os.Exit(1)
 		}
 	}