Lobby: Fix Password Entry

Summary

The new WebSocket-based lobby calls the REST /start endpoint automatically on mount, before the guest has entered a password. For password-protected rooms this always fails with WrongRoomPassword, shows a "password incorrect" toast and transitions to FailedCredentials, which permanently disables the Enter now button.

This change defers /start until the guest submits the password, keeps the button retriable and auto-sends the enter command once the lobby is reached so joining stays a single click.

Implementation Tasks

• Skip auto-connect for password-protected rooms - open connection on submit instead
• Keep the submit button enabled in Setup / FailedCredentials so guests can retry without reloading
• Auto-send the enter command once the deferred start reaches Lobby (single click)
• Dismiss the "wrong password" toast on successful start
• Add unit tests for deferred start, validation, retry and auto-enter