docs: record Parent Call, the DVD migration and what is left to test

Three things in this window that a container cannot answer, and they are
now the top of the next-steps list: a real key pressed into Parent Call,
a television switched on after the computer, and a disc that plays.

Also brings the comments in the shared libraries up to date. The only
mention of sway left in the tree is the upgrade step that removes the
sway-era login shell from a room being upgraded.

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

scripts/classroom-dvd-session

@@ -79,8 +79,9 @@ LEAVE_HIDE_SECONDS = 1
 
 # How long the cover stays up at the very least.
 #
-# This replaced a query to the window manager. Under sway the session
-# walked the tree until VLC's window was really fullscreen, because VLC
+# This replaced a query to the window manager. The session used to walk
+# the compositor's tree until VLC's window was really fullscreen, because
+# VLC
 # reports playing while its window is still the ordinary one — the black
 # startup window the cover exists to hide.
 #