feat: give every room the broker, one scale, and its own panel back

Little Waders took the Plasma build and reported what a container
cannot. A disc player on a machine with no optical drive, a clock nobody
at the back of the room could read, a browser at half the size of the
panel around it, and Parent Call with no broker to call.

The broker is the same for every classroom, so it is a default now and
not something to fill in room by room. classroom-migrate brings an
existing room to the same place without touching its name, its username
or its password, and Parent Call distinguishes a broker it cannot reach
from one that was never set up: those send somebody to look at
completely different things.

The disc player's detection was right and ran too late — alongside the
session rather than before it, and the panel is built from the layout the
moment a session starts. It runs before the display manager now, and
again from udev when a drive is plugged in.

UI_SCALE had a ceiling of 1.5, which cannot express a 4K television; a
clock pinned at 15 points, which is the same size at every scale; and a
browser that was never told the number at all. All three are fixed and
the room doubles together at 200%.

This also brings 0.1.47's work into the repository, where it had only
ever existed in a build directory under /tmp: the hidden display dialog,
its authenticated writer, the polkit action, and the church's own
wallpaper. One piece of it is deliberately left out. The custom volume
display needed a shell package of our own, and with one selected
plasmashell builds no panel at all — measured twice, with that build's
own files, on a classroom that deletes its panel configuration at every
login by design.

The lab connected to the real church broker the moment the package
defaulted to it. Nothing was left behind, which was checked, but the
guard that should have stopped it had never worked: it used iptables,
which the lab image does not have, and probed with /dev/tcp under dash,
where that always fails. Both reported success.

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

config/plasma/lookandfeel/contents/layouts/org.kde.plasma.desktop-layout.js

@@ -123,7 +123,23 @@ rightGap.writeConfig("expanding", true);
 // about. Naming the four the classroom actually uses is both smaller and
 // deterministic, and it leaves nothing for a teacher to expand.
 panel.addWidget("org.kde.plasma.networkmanagement");
-panel.addWidget("org.kde.plasma.volume");
+
+var volume = panel.addWidget("org.kde.plasma.volume");
+volume.currentConfigGroup = ["General"];
+// No chime when the volume changes. A classroom is often listening to
+// something when somebody adjusts it, and a beep over a lesson is worse
+// than no feedback at all — the on-screen display is the feedback, and it
+// is in the look and feel package where a television can read it.
+//
+// Plasma 6 moved this setting out of the applet and into a global one,
+// and the applet migrates a false written here into it on first run. So
+// this is both the setting and the instruction to carry it across.
+volume.writeConfig("volumeFeedback", false);
+volume.writeConfig("volumeOsd", true);
+volume.writeConfig("muteOsd", true);
+volume.writeConfig("outputChangeOsd", true);
+// A teacher pressing the volume key expects a step they can hear.
+volume.writeConfig("volumeStep", 5);
 
 panel.addWidget("org.kde.plasma.notifications");
 
@@ -134,8 +150,13 @@ clock.writeConfig("dateFormat", "custom");
 clock.writeConfig("customDateFormat", "ddd d MMM");
 clock.writeConfig("showSeconds", 0);
 clock.writeConfig("dateDisplayFormat", "BelowTime");
-// Left to itself the clock grows to the height of the bar and becomes the
-// largest text in the room. It is status, not a headline.
-clock.writeConfig("autoFontAndSize", false);
-clock.writeConfig("fontSize", 15);
+// Sized by the bar, not by a number written here.
+//
+// It used to be pinned at 15 points to stop it becoming the largest text
+// in the room. On a 4K television that was a clock a teacher could not
+// read from the back of the room, and it was the one thing in the
+// classroom that did not follow UI_SCALE, because a point size written
+// into a layout is the same point size at every scale. Plasma's own
+// sizing follows the bar, and the bar follows the scale.
+clock.writeConfig("autoFontAndSize", true);
 clock.writeConfig("fontWeight", 500);