docs: the Wi-Fi hand-over is a physical check, so write down its steps

No lab has the laptop's radio, so the one thing that cannot be proven
here is the hand-over succeeding. These are the ten steps that prove it
on the machine, including the four that prove the classroom account
still cannot read the password afterwards.

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

docs/testing.md

@@ -323,6 +323,35 @@ DVD_ENABLED=false
 Nothing about `DEVICE_TYPE=laptop` turns those applications off; they are
 off because those lines say so.
 
+### Physical verification — the Wi-Fi hand-over
+
+No lab can do this one: it needs the laptop's radio. Over SSH, watching,
+with a way back into the room if it goes wrong:
+
+1. `classroom-wifi --check` — expect it to name the interface and say
+   ifupdown owns it. Changes nothing.
+2. `classroom-wifi --adopt --dry-run` — expect the three "would" lines.
+   Changes nothing. `/etc/network/interfaces` must still be identical.
+3. `classroom-wifi --adopt`. It prints each step. Expect it to end with
+   *"is NetworkManager's now, and the room is online"*.
+   If it fails it puts ifupdown back by itself and says so; the machine
+   should still be reachable. `classroom-wifi --rollback` undoes it later.
+4. `nmcli device status` — the Wi-Fi device must no longer say
+   `unmanaged`.
+5. `nmcli networking connectivity` — must say `full`, not `none`.
+6. `nmcli device wifi list` — must now list networks.
+7. Log out and back in. The panel must show the Wi-Fi connection.
+8. Reboot. It must reconnect on its own, with nobody typing a password.
+9. As the **classroom** account, confirm the password is still
+   unreachable:
+   - `nmcli -s -g 802-11-wireless-security.psk connection show <name>`
+     must be empty
+   - the applet's *Show Network's QR Code* must not produce one
+   - `/etc/NetworkManager/system-connections/*.nmconnection` must be
+     unreadable
+10. As **tech**, confirm maintenance still works: `sudo nmcli -s ...`
+    returns the key.
+
 ### Physical verification — a real lid and a real television
 
 The lab has no lid and no HDMI hotplug, so none of this is proven by a