feat: settle Chrome's window, crash bubble and password prompts

Three things a volunteer should never have to see.

Sway was drawing its own title bar above Chrome's tab strip, which
already carries the window controls. Verified on a real session: Chrome
is an xdg_shell client with app_id "google-chrome" and sway was giving
it border "normal". A scoped rule removes the compositor decoration
only — Chrome keeps its tabs and address bar, stays a normal window, and
still maximises and minimises. A class rule covers an XWayland fallback.
Nothing else changes: the only other window in this classroom is VLC,
which is already borderless, so no broader rule is warranted.

"Restore pages? Chrome didn't shut down correctly" is suppressed with
--hide-crash-restore-bubble. Note the name. The switch this was going to
use, --disable-session-crashed-bubble, is not present in Chrome 152 at
all — checked against the strings of the installed binary — so it would
have silently done nothing.

That hides the prompt; the profile was still being marked as crashed,
which is the untidy half. Chrome's browser process shuts down cleanly on
SIGTERM, so a shutdown unit now gives it one and waits up to eight
seconds before the session is torn out from under it. Best effort by
construction: a shutdown that will not finish is far worse than a crash
flag.

Password prompts go off with the PasswordManagerEnabled policy, on the
path the classroom already manages. Existing profile and session data
are untouched, and website logins are unaffected: Wonder Ink and YouTube
stay signed in.

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

tools/build-release.sh

@@ -125,6 +125,10 @@ install -Dm755 \
     "$ROOT/scripts/classroom-scale" \
     "$STAGE/usr/local/bin/classroom-scale"
 
+install -Dm755 \
+    "$ROOT/scripts/classroom-shutdown" \
+    "$STAGE/usr/local/bin/classroom-shutdown"
+
 install -Dm755 \
     "$ROOT/scripts/classroom-chrome-setup" \
     "$STAGE/usr/local/bin/classroom-chrome-setup"
@@ -203,6 +207,10 @@ install -Dm644 \
     "$ROOT/systemd/provision/ekklesia-classroom-provision.service" \
     "$STAGE/etc/systemd/system/ekklesia-classroom-provision.service"
 
+install -Dm644 \
+    "$ROOT/systemd/shutdown/ekklesia-classroom-shutdown.service" \
+    "$STAGE/etc/systemd/system/ekklesia-classroom-shutdown.service"
+
 install -Dm644 \
     "$ROOT/config/icons/dvd.svg" \
     "$STAGE/etc/ekklesia-classroom/icons/dvd.svg"