docs: write up the classroom v2 result

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

tools/lab/Dockerfile.plasma

@@ -70,3 +70,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
       pipewire pipewire-pulse wireplumber pulseaudio-utils \
       libnotify-bin \
  && rm -rf /var/lib/apt/lists/*
+
+# seatd, so wlroots can open input devices without a login session. The lab
+# compositor needs a seat before it can offer the session under test a
+# pointer to be clicked with.
+RUN apt-get update && apt-get install -y --no-install-recommends seatd \
+ && rm -rf /var/lib/apt/lists/*