Improve workshop checkout and cost-centre funding

[nomadjimbob]

Combined workshop and store purchases now use one invoice and one booking confirmation email. Payment receipts retain the ticket and Store Order references without repeating purchased items, and customers can start another ticket purchase after completing an earlier checkout.

• Simplify the booking email, with HTML and plain-text versions that adapt to ticket quantity, payment status, attachments, and optional Store Orders.
• Hide shipping address fields for collection and show the same collection notice as the store checkout.
• Display the reservation countdown in the top-right corner throughout checkout. Workshops with optional equipment get 20-minute holds across payment validation, availability, early-bird calculations, and cleanup; other workshops retain their configured duration.
• Include the branch’s existing remuneration funding changes, allowing forgone remuneration to fund cost centres.
• Add remembered-device regression coverage and update the notification test to expect the normal success alert.

Validation:

• php artisan qa --without-tty: 1,065 tests / 9,834 assertions passed; PHPStan passed; Composer and npm audits reported no vulnerabilities.
• node --test tests/Browser/*.test.cjs: all 135 tests passed.
• npm run build and git diff --check passed.

Deployment requires the included migrations for the ticket-email Store Order link and remuneration fund transfers.