Add Security & Pre-Deploy Checks section

[mpvasilis]

What

Adds a new Security & Pre-Deploy Checks section. Vibe-coded apps frequently ship with exposed secrets, world-readable databases, or missing security headers — but the list had no section covering pre-deploy security. This fills that gap.

Entries (3, distinct angles)

• Vibeproof — instant security scan for vibe-coded apps (Lovable/Bolt/v0/Cursor); URL or public repo, free, no signup.
• Snyk — code/dependency/IaC vulnerability scanning (free tier).
• Mozilla HTTP Observatory — free security-headers grading.

Also added the corresponding entry to the Contents table. Formatting matches existing entries (- [Name](url) - Description.).

Disclosure: I'm involved with Vibeproof, but seeded the section with two well-established independent tools so it stands as a genuine category rather than a single product link. Happy to adjust wording or entries.