Staff can lock a section (or the whole event) to their device, download
its tickets and keep scanning with no connection. Scans are queued in
IndexedDB and synced idempotently when back online; conflicts go into a
sync report for supervisors, who can also force-release a lost device.
The server now validates scan sections and refuses scans in a scope
locked to another device. Adds a web app manifest and a service worker
for the scanner page.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>