fix: let an update change the Parent Call button

Two findings, both from watching the bar refuse to change.

The Icon widget copies the desktop entry into the user's home and uses
the copy. A classroom that had already run kept the old icon and the old
command for ever: the package no longer contained a bell and the bar kept
showing one. The button is a task manager holding a single launcher now,
which resolves /usr/share/applications live — the place an OTA update
writes to — and costs nothing, because the classroom already runs one for
the applications.

NoDisplay=true then hid the entry from the very index that resolves
launchers, and the bar drew a blank page. There is no application menu in
this classroom for the entry to clutter, so it is indexable now.

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

config/plasma/applications/ekklesia-parent-call.desktop

@@ -17,6 +17,9 @@ Terminal=false
 Categories=Utility;
 StartupNotify=true
 StartupWMClass=classroom-parent-call
-# Never in an application list. It is reached from the bar, and it is not
-# one of the room's applications.
-NoDisplay=true
+# Deliberately visible to the applications index. NoDisplay=true hid it
+# from the index the panel resolves launchers through, and the bar showed
+# a blank page instead of the mark. There is no application menu in this
+# classroom for it to clutter — no Kickoff, and KRunner is off — so being
+# in the index costs nothing.
+NoDisplay=false