Add 5 MiN8T free tools to Tools + Testing sections

[Davison-Francis]

Hi! Adding 5 entries from the MiN8T free-tools collection - all browser-based, no signup, no upload.

Tools section (4 entries)

• CSS Inliner - in-browser CSS inliner that preserves @media, @keyframes, and pseudo-class rules. Direct counterpart to Alter.email already in the list.
• MJML to HTML - in-browser MJML compiler with live iframe preview. Companion to the MJML Desktop App already listed.
• Bulletproof Button Generator - ships the full VML fallback for Outlook desktop (not just the modern-CSS half). Spiritual successor to buttons.cm.
• Subject Line Analyzer - real-time scoring on length, spam triggers, sentiment, emoji, caps, personalization tokens.

Testing section (1 entry)

• Spam Score Checker - 21-rule SpamAssassin-style scoring with per-rule breakdown. Free + unlimited (mail-tester is free up to 3/day).

All five fit gaps in the existing list. Each uses the standard [Name](url) - Description format. Happy to trim or split into smaller PRs if preferred.

Thanks for maintaining this list — it's the canonical email-dev resource.

[Davison-Francis]

Quick disclosure I should have flagged up front — I'm associated with MiN8T, so this is a contributor-affiliated submission rather than a third-party recommendation.

If five entries from one source feels like too many, happy to trim to whichever 1-2 you think fit the list best, or split into single-tool PRs. Whatever shape works for you.