feat: add CSRF token validation for critical operations #13

Medium Priority#

Location: All POST/PUT/DELETE endpoints in src/index.ts

Issue#

No CSRF token validation on state-changing operations (relies on SameSite cookies only)

Impact#

Reduced protection against CSRF attacks

Fix Time#

~2 hours

Recommendation#

SameSite=Lax provides some protection, but consider adding CSRF tokens for critical operations

From LAUNCH_REVIEW.md Issue #23