Guest play, settings, and sound

Added

• Guest sessions let anyone play without an account.
• A settings screen controls music and SFX volume, and background music plays on every screen outside the match.
• The rule catalog now comes from the server, so new rules appear on their own.
• A profanity filter covers 28 languages and blocks profane usernames at registration.

Changed

• The landing and lobby browse screens get a responsive redesign built from reusable components.
• Connection errors read as plain messages, and browse keeps its lobby list fresh.