Visitor sign in kiosk: multi-site, badge printing, WWCC expiry warnings, admin accounts with 2FA

.env.example

@@ -67,7 +67,6 @@ SHEETS_ENABLED=false
 # The long id from the sheet URL: docs.google.com/spreadsheets/d/<THIS PART>/edit
 SHEETS_SPREADSHEET_ID=
 # Append-only history of every sign in and sign out.
-SHEETS_LOG_TAB=Visitor log
 # Rewritten on every change: only the people currently on site. Open this one
 # during an evacuation. Both tabs are created automatically if missing.
 SHEETS_ONSITE_TAB=On site now