Replace default auto-generated password with a first-run setup page that
lets users choose their own nickname and password. The /auth/setup endpoint
now accepts an optional nickname field (also sets site_name). Remove
set_default_password() since setup is now mandatory before login.
passlib 1.7.4 has a known bug with bcrypt 4.x on Python 3.13 where
detect_wrap_bug passes an over-72-byte hash as a password, causing
ValueError on every login attempt.
Switched to bcrypt.hashpw/checkpw directly, removing the passlib
dependency entirely.
Also fixed 401 page reload on /auth/login endpoint.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>