feat(screening): implement fast ViT screening with zero-retention ephemeral purge and 10MB payload boundary (Story 1.1)

Disable PostgreSQL database connections on Hugging Face Spaces

Implement registration role request, register link in login form, and background email alerts to sales@freshbeats.ai on login/registration

fix: make psycopg2 optional and support SQLite fallback for user auth on HF Spaces

Initial clean commit of modular MorphGuard