fix(other): email validation require fqdn tld

[IrAlfred]

Fix email validation and add RFC 5322 compliance

Issue

• Email addresses without proper TLD were accepted (e.g., alfred@test, patrick@example)
• Valid RFC 5322 formats were rejected (IPv6 addresses, quoted strings, internationalized domains)

Changes: Added RFC 5322 compliant validation

• Client-side: modules/core/site.js, modules/smtp/site.js
• Server-side: modules/core/functions.php
• Support for domain literals (IPv4/IPv6), quoted local-parts, IDN, group syntax
• Enforces minimum 2 domain labels (fixes TLD issue)

[IrAlfred]

In fact, the is_valid_recipient function, used on the Compose page for example, uses different validation logic compared to a simple email field on the contact form, which only accepts the email address. It must accept these different formats:

• Display Name <email@example.com>,
• Display Name email@example.com, or
• email@example.com