Split login name and trip key fields

[mitdok]

Summary

• Add a generated login form with separate name and trip-key inputs on room pages
• Keep the WebSocket login payload compatible with the current backend by sending name#tripKey when the trip-key field is filled
• Preserve the legacy name#key form when entered directly in the name field
• Update the authenticated-room help text to explain the separated fields

Notes

• This version does not require a backend deploy because it still uses the existing backend login parser.
• The later monorepo can clean this up into a JSON protocol once frontend and backend are changed together.