fix: a notification's Configure button no longer opens system settings

The kernel memory killer's "Memory Shortage Avoided" notice carried a
Configure button that ran kcmshell6 and opened KDE's whole Notifications
settings under the teacher's account. Reproduced in the lab.

Plasma draws that button without consulting the Kiosk policy, but
kcmshell6 and System Settings do: every settings module Debian 13's
Plasma 6.3 installs (90) is now refused in the classroom's immutable
kdeglobals, so the same click shows only "disabled by the system
administrator". The clock's Configure Digital Clock goes with
plasma/allow_configure_when_locked=false; Configure Audio Devices
disappears on its own; the disabled window's Help button opened KDE Help
Center, which the package now conflicts with (plasma-desktop only
recommends it).

The maintenance terminal runs outside the classroom's configuration and
still opens every module, verified. converged-check fails if any module
on a machine is ever left unrestricted: 126 passed in the lab.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

tests/test-deployment-support.sh

@@ -197,6 +197,16 @@ for restriction in ("run_command=false", "shell_access=false",
                     "action/lock_screen=false",
                     "plasma/plasmashell/unlockedDesktop=false"):
     check(f"{restriction}", restriction in restrictions)
+check("a notification's Configure button opens nothing",
+      "kcm_notifications=false" in restrictions)
+check("and neither does any other settings module a teacher might reach",
+      all(f"{m}=false" in restrictions for m in (
+          "kcm_pulseaudio", "kcm_clock", "kcm_kscreen", "kcm_users",
+          "kcm_sddm", "kcm_keys", "kcm_bluetooth", "kcm_powerdevilprofilesconfig")))
+check("a locked panel offers no widget settings",
+      "plasma/allow_configure_when_locked=false" in restrictions)
+check("and the help center a settings window's Help button opens is not installed",
+      "khelpcenter" in re.search(r"^Conflicts: (.*)$", control, re.MULTILINE).group(1))
 check("the restrictions are immutable", "[KDE Action Restrictions][$i]" in restrictions)
 
 print()