docs: the power button, the maintenance chord, and why long-Escape should change

Records what was measured this pass and, as importantly, what was not.

KGlobalAccel will accept a bare Escape and its component carries both a
pressed and a released signal, so hold-and-cancel is expressible. What
could not be measured here is whether a global shortcut takes the key
away from applications, because key injection cannot reach the nested
session. The mechanism says it does — KWin matches shortcuts in an input
filter ahead of the focused surface — which would cost the classroom
every ordinary use of Escape. That is inference, and it is written down
as inference, with the thirty-second bench test that settles it.

The recommendation is to change the gesture rather than grab the key an
appliance uses most: hold-to-confirm on an on-screen control, which is
ordinary Qt inside our own surface, or a modifier chord like the one the
maintenance terminal just proved. Either keeps the deliberate ceremony
without an input daemon.

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

docs/screenshots/README.md

@@ -59,6 +59,13 @@ container lab. See [../classroom-v2-experiment.md](../classroom-v2-experiment.md
 | `v2-layershell` | a gtk-layer-shell overlay under KWin — what the DVD loading cover is made of |
 | `v2-notification-crop` | a notification card, top right |
 
+## Administration
+
+| | |
+| --- | --- |
+| `admin-terminal` | the maintenance terminal, opened by its chord's action |
+| `admin-terminal-bar` | the bar with the terminal open, and after closing it: a task button while it runs, no launcher ever |
+
 ## Reliability and lockdown
 
 | | |