Add MailKite SaaS Starter to SaaS section

[bucabay]

Hi 👋

Added MailKite SaaS Starter to the ## SaaS section (appended at the end, matching the existing - [Name](url) - Description. format).

It's a production-ready, MIT-licensed Next.js 15 SaaS starter. What makes it a good fit for this list:

• Self-contained auth — Google/GitHub OAuth + email/password implemented in-app (JWT/sessions), so there's no Clerk / Auth0 / Supabase-Auth account required. Clone, add your own OAuth app, ship.
• Stripe subscriptions + teams, Postgres/Drizzle, and a dark-first shadcn/ui dashboard.
• Live demo: https://saas-startup.mailkite.dev

Happy to adjust the wording or placement if you'd prefer. Thanks for maintaining the list! 🙏