fix: keep the DVD player whole

Removing gtk-layer-shell from the dependencies broke classroom-dvd on the
first run, and deleting the dock's stylesheet took the DVD control bar's
styling with it. Both go back: the template under a name that says what
still uses it, and the dependency with a line in the package description
explaining that it is there for the disc player and not for a dock.

A probe overlay confirms gtk-layer-shell works under KWin, so the loading
cover survives the move. The focus helper still speaks sway, which is
written down rather than papered over.

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

lib/classroom_style.py

@@ -8,7 +8,7 @@ from pathlib import Path
 
 from classroom_config import scaled
 
-TEMPLATE = Path("/etc/ekklesia-classroom/dock/style.css.in")
+TEMPLATE = Path("/etc/ekklesia-classroom/overlay/style.css.in")
 
 # Every measurement in the template, at UI_SCALE=1.0.
 MEASUREMENTS = {