Opt into Flatpak progress reporting now that we support the relevant escape sequences

Sets FLATPAK_TTY_PROGRESS in the environment, cf. [1]

[1] https://feaneron.com/2025/01/14/flatpak-1-16-is-out/progre

src/session/Session.cpp

@@ -590,6 +590,8 @@ void Session::run()
     secretEnv << QStringLiteral("KONSOLE_DBUS_ACTIVATION_COOKIE=%1").arg(m_activationCookie);
 #endif
 
+    addEnvironmentEntry(QStringLiteral("FLATPAK_TTY_PROGRESS=1"));
+
     // stuff set via addEnvironmentEntry and the secret parts
     const QStringList fullEnv = _environment + secretEnv;