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/dbus/fr.emersion.mako.service

@@ -0,0 +1,22 @@
+[D-BUS Service]
+# The old notification daemon, made unstartable.
+#
+# Removing mako's activation from systemd was not enough, and this was
+# measured rather than guessed: during the crash-recovery test on a
+# migrated machine, the panel was killed, something in the session sent a
+# notification while nothing owned org.freedesktop.Notifications, and
+# D-Bus started mako from the file mako-notifier ships. The room would
+# then have had the old shell's popups on a Plasma desktop, from a daemon
+# with no configuration, until the next reboot.
+#
+# This file shadows that one. The session bus searches XDG_DATA_DIRS in
+# order and /usr/local/share comes before /usr/share, which is the same
+# mechanism the classroom already uses to shadow a desktop entry — no
+# Debian file is touched, and mako-notifier can be upgraded or removed
+# without any of this needing to change.
+#
+# /bin/false is what a machine with no notification daemon installed does
+# anyway: the activation fails and the caller is told so. Plasma's own
+# service takes the name at startup and never comes through here.
+Name=org.freedesktop.Notifications
+Exec=/bin/false