Proposal: Add domain() validator to Valibot

Summary

Add a built-in domain() validator to Valibot for validating FQDNs and second-level+ domains, with configurable options (Unicode/IDNA, TLD filtering, wildcard, trailing dot, etc.). This covers the common case “validate a domain, not a URL/email/localhost” without having to maintain complex regular expressions.

Prior discussions that were closed:

• PR that attempted to add this feature but was closed without a clear explanation: feat: add domain name action #907
• Issue that was auto-closed due to inactivity: improvement : add domain name validation #894

Please consider adding this validator to core or to an official extensions package.

Problem

Valibot provides email() and url(), but there is no validator specifically for domain names. As a result:

• Consumers fall back to regex()/pattern(), which is:
  • hard to maintain and reuse,
  • easy to get wrong on edge cases (label length 1–63, overall length, hyphen rules, IDNA/Unicode, TLD constraints, etc.).
• url() is too broad when only a bare domain (no scheme/path/port) is needed.