Recognition starts with the app, not with a button

The engine only ever started when somebody pressed Start. So a till
that rebooted overnight came back with the window open, the tray icon
showing, the session restored - and recognition off until a shop
assistant noticed. That is the failure the tray colours exist to catch,
and it should not be the default state every morning.

Guarded on the interpreter actually existing: on a PC where setup has
not run yet, the supervisor would loop on a missing executable with
nothing useful to say. Start and Stop remain for the case where somebody
has deliberately stopped it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KGcjxF1cNLcuwc3DAPcnfj

desktop/app.go

@@ -124,6 +124,23 @@ func (a *App) startup(ctx context.Context) {
 	})
 
 	a.startPipeline(ctx)
+
+	// Recognition starts with the app. Until this, the engine only ever
+	// started when somebody pressed Start - which meant a till that rebooted
+	// overnight came back with the window open, the tray icon showing, the
+	// session restored, and recognition off until a shop assistant noticed.
+	// That is the failure the tray colours exist to catch, and it should not
+	// be the default state every morning.
+	//
+	// Guarded on the interpreter actually being there: on a PC where setup has
+	// not run yet, starting the supervisor would loop on a missing executable
+	// with nothing useful to say. The Start button still exists for the one
+	// case where somebody has deliberately stopped it.
+	if _, err := os.Stat(exe); err == nil {
+		a.sup.Start()
+	} else {
+		log.Printf("engine not installed yet (%s); run behavision-setup, then Start", exe)
+	}
 }
 
 // webhookURL is the loopback address the bridge is listening on, or empty