fix: make an existing classroom converge into the Plasma appliance

A real room upgraded to 0.1.45 and came up as stock Debian Plasma with
the old Waybar across the top, mako still catching notifications, and a
lock screen on an account that has no password.

The cause was one line, and it was in the lab: the harness handed the
session under test XDG_CONFIG_DIRS by hand, so every result it had ever
produced was a result about a machine somebody had already configured.
On a machine SDDM starts the session through PAM, PAM does not read
/etc/environment.d, and Debian's own plasma-workspace env.sh then set the
variable from scratch — so the classroom's settings directory was not in
the cascade at all. No layout, no lock policy, no Kiosk restrictions.

The settings now arrive the way Plasma delivers them, through a file in
/etc/xdg/plasma-workspace/env. Around that: the look and feel is
immutable on its own key so a stale profile cannot answer for it; the
palette is composed into the package, because naming a colour scheme does
not produce one and the dark bar had been coming from a technician's
hand; the desktop reset converges another desktop's appearance state and
keeps the room's own; and classroom-migrate stops, deactivates and masks
the old shell, including the D-Bus activation that brought mako back
while the panel was down — found only by killing the panel on a migrated
machine.

device.conf loses COMPOSITOR and comes off the hyprland channel, which
would otherwise have handed the room the experiment back.

The lab stops flattering the package: it restarts the machine, lets SDDM
actually autologin, and asks a fresh install and a machine upgraded from
the Hyprland package the same sixty questions. Both answer identically,
twice, and the panel still comes back from eight SIGKILLs.

Co-Authored-By: Claude Opus 5 <[email protected]>

config/plasma/xdg/kdeglobals

@@ -48,7 +48,18 @@ XftSubPixel=rgb
 
 [KDE]
 widgetStyle=Breeze
-LookAndFeelPackage=org.ekklesia.classroom.desktop
+# One key, marked immutable on its own rather than by freezing the group.
+#
+# This is the name plasmashell reads to decide which layout script builds a
+# panel for a session that has none, so it decides whether the room comes
+# up as the classroom or as stock Plasma. A migrated machine reached this
+# experiment with a user profile that had been through other desktops, and
+# a user's own kdeglobals sits ahead of every system directory in the
+# cascade. Immutable here means no leftover profile, and no stray write by
+# a settings dialog that does not exist in this room anyway, can answer
+# that question differently. The palette below stays writable, because
+# classroom-theme is allowed to change it.
+LookAndFeelPackage[$i]=org.ekklesia.classroom.desktop
 SingleClick=false
 AnimationDurationFactor=0.5