Fix: no-args should start TUI, not print help

The condition showHelp||len(filtered)==0 caused the tool to always
print usage and exit. Now only --help triggers usage+exit.

cmd/kctl-tui/main.go

@@ -40,10 +40,13 @@ func main() {
 		kubeexec.SetVerbose(true, os.Stderr)
 	}
 
-	if showHelp || len(filtered) == 0 {
+	if showHelp {
 		printUsage()
 		return
 	}
+	if len(filtered) == 0 {
+		// No subcommand — start the full TUI.
+	}
 
 	if len(filtered) > 0 {
 		switch filtered[0] {