- L-01: Setup endpoint used scalar_one_or_none() on unbounded User
query, throwing 500 MultipleResultsFound when >1 user exists.
Replaced with select(func.count()) for a reliable check.
- L-02: Change-password allowed reusing the same password, defeating
must_change_password enforcement. Added equality check before
accepting the new password.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>