docs(cmd): clarify why !noTUI branch prints the fallback notice

cmd/archduino/main.go

@@ -72,9 +72,12 @@ func newInstallCmd() *cobra.Command {
 			}
 
 			reporter := engine.NewPlainReporter(os.Stdout)
+			// When the user did NOT opt out of TUI (the default), note that
+			// the TUI isn't implemented yet and we're falling back to plain
+			// output. Plan 2 wires up Bubble Tea here; at that point this
+			// branch becomes the TUI setup and the PlainReporter above moves
+			// inside the `noTUI` branch.
 			if !noTUI {
-				// Plan 2 replaces this with the Bubble Tea dashboard. For now
-				// the plain reporter is the only surface.
 				fmt.Fprintln(os.Stdout, "(TUI not yet implemented — using plain output)")
 			}