Issue #3614048: Translate the reworded check-in camera fallback messages and drop the dead check-in field strings

Two check-in messages fell through untranslated on a French site, and they are exactly the ones a door operator sees when the camera cannot open.

The messages were reworded in checkin.js when the check-in screen was reworked, and the translation never followed, so translations/yoyaku.fr.po still carried the pre-rework msgids. Those match nothing in the source, so both strings render in English. They also described a field the operator can no longer type into.

This updates both entries in place to the current source wording:

.po carried (matched nothing)	current source
Camera scanning is not available here; scan or type the code into the field.	Camera scanning is not available in this browser. Open the ticket QR with your device camera app instead.
Camera unavailable; scan or type the code into the field.	Camera unavailable. Open the ticket QR with your device camera app instead.

It also drops two msgids dead for the same reason: Ticket code and Point the camera at the ticket QR, or type / scan the code and submit. both labelled the visible code field that #3613083 replaced with an opaque hash nobody types.

Why it was missed

The translation coverage checks run before this only extracted from PHP and YAML. Re-running with Drupal.t() in JavaScript and the t filter in Twig added to the extraction is what surfaced the gap. Coverage across the channels a module .po owns is now complete:

Channel	Strings	Missing
PHP t() / TranslatableMarkup	780	0
PHP formatPlural()	43	0
JavaScript Drupal.t()	55	0
JavaScript Drupal.formatPlural()	7	0
Twig |t	9	0
Menu links	46	0
Permissions	13	0
Route titles	8	0

msgfmt --check-format passes.