Adds Next.js Waitlist with Double Opt-In and a Bulk Launch Email (Mailtrap) under JavaScript > Next.js.

• Author disclosure: I'm not the author. It is by @Sid-Lais, and I've contributed to it (merged PR #1).
• Free and open: MIT-licensed, public, no paywall or signup.
• What the reader builds: a working Next.js waitlist with double opt-in confirmation emails, a referral queue and a bulk launch email with one-click unsubscribe, sent through the Mailtrap Email API, using TypeScript, Drizzle and SQLite. The README walks through the setup, the flow and the key code.
• Honest scope note: it is a documented project with a README walkthrough rather than a multi-part written tutorial. If that is out of scope for this list, I'm happy to withdraw the pull request.

Checks: python3 scripts/check_readme.py lint exits 0 (errors=0, warnings=0), and the entry uses the - [Title](link) format with a direct link.