- Adds UI links for joining with PIN in Login and Register pages.
- Normalizes event slugs to lowercase (preserving hyphens) and event PINs to strip all hyphens/spaces to handle raw inputs.
- Implements a pre-check rate limit pattern (`isRateLimited`) to safely enforce a max of 5 failed attempts per IP window (60s) without rate-limiting successful authentications.
- Achieves NAT-safe idempotency in `POST /api/join` by extracting and reusing active event guest sessions instead of blindly incrementing claimed seats on every request.
- Integrates complete test suite coverage for these new constraints.
Co-authored-by: mrteye <1945243+mrteye@users.noreply.github.com>
