- TestLoadCSRFKey_* in internal/auth for env key loading
- TestCSRF_*MissingToken / TestCSRF_*ValidToken for all three POST routes
- TestForms_ContainCSRFField for hidden _csrf input in rendered HTML
- TestRouter_CSRFMountedAfterResolveSession for middleware order (D-24)
- TestCSRF_HeaderFallback for X-CSRF-Token header support
- Add gorilla/csrf v1.7.3 dependency