Update Mailer related dependencies

[KabinKhandThakuri]

• Bump nodemailer from 7.0.13 to 9.0.3 — no API changes affecting this plugin (plain SMTP transport)
• Bump html-to-text from 9.0.5 to 10.0.0 — used indirectly via nodemailer plugin
• Bump mjml from 4.18.0 to 5.4.0 — major breaking changes required source fixes
• Bump @types/nodemailer from 6.4.24 to 8.0.1
• Bump @types/mjml from 4.7.4 to 5.0.0
• packages/mailer/src/plugin.ts — Added mjmlOptions: { validationLevel: "soft" } to nodemailerMjmlPlugin() call. MJML v5 introduced PostCSS processing that throws CssSyntaxError on mustache {{ }} template syntax in CSS blocks. validationLevel: "soft" allows this syntax to pass through.
• packages/mailer/src/router.ts — Added await to mjml2html() call. MJML v5 changed mjml2html() from synchronous to async. Without await , the result was a Promise object instead of compiled HTML, causing the test route to send emails with no body.
• packages/mailer/src/test/registration.test.ts — Updated test expectation to include the new mjmlOptions parameter passed to nodemailerMjmlPlugin .