feat: minimize and restore windows the way a desktop does

The scratchpad technically minimized Chrome, but sway hands scratchpad
windows back floating, so restoring gave a draggable window instead of
the maximized one the user put away. Park windows on a hidden workspace
as ordinary tiled containers instead, and move them back to the visible
workspace on restore.

classroom-window carries the whole state machine, so the dock buttons
and Super+M share one implementation:

  not running  -> launch
  unfocused    -> focus
  focused      -> minimize
  minimized    -> restore, tiled and maximized

Fullscreen is dropped on the way out, since a container parked while
still fullscreen keeps drawing over everything else. floating disable on
the way back also rescues windows left floating by the old scratchpad
path.

Super+Shift+M restores the newest minimized window, so nothing can get
stranded on the hidden workspace.

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

packaging/debian/postinst

@@ -18,6 +18,7 @@ chown classroom:classroom /home/classroom/.bash_profile
 chmod 0644 /home/classroom/.bash_profile
 
 chmod 0755 /usr/local/bin/classroom-browser
+chmod 0755 /usr/local/bin/classroom-window
 
 if [ ! -f /etc/ekklesia-classroom/device.conf ]; then
     cat > /etc/ekklesia-classroom/device.conf <<'CONFIG'