Security: remove auto-login demo endpoint, require password for demo_user

Fix: add read permission to demo_user for tree access

refactor: Clean up and rename to Demo Account

feat: Replace complex auto-login with simple Conference Demo button

feat: Add conference auto-login with demo participant role

feat(telemetry): add admin UI, server/client auth telemetry; grant admin to Ishita

Complete async database operations and codebase cleanup

fix: Replace pbkdf2_hex with pbkdf2_hmac for correct hash function

security: Remove all hardcoded passwords from codebase and documentation

feat: Update user accounts with personalized credentials

feat: Add comprehensive authentication system with user management