Add room name moderation/filtering

Public room names should be filtered or moderated to avoid slurs and sexual references.

Feedback source:
- "A room name filter may be a good add, just opened the site to see a few rooms containing slurs and/or sexual references in their names."

Acceptance ideas:
- Validate room names on create/update.
- Return clear validation errors for disallowed names.
- Consider server-side enforcement so clients cannot bypass it.
- Keep the filter simple and maintainable.