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]>

lib/classroom_vlc.py

@@ -65,7 +65,8 @@ CLASSROOM_HOTKEYS = {
 
 # VLC dressed down to a playback surface. Verified against 3.0.23.
 PRESENTATION = (
-    # DVD mode is the whole display, and sway fullscreens the window the
+    # DVD mode is the whole display, and the compositor fullscreens the
+    # window the
     # moment it maps so no wallpaper is ever visible around it.
     "--fullscreen",
     # No menu bar, no panels, dark rather than light grey.