Bcrypt silently truncates passwords at 72 bytes, so passwords longer than 72
characters provide no additional security. This commit enforces the 72-byte
maximum across the authentication and setup flows.
Changes:
- Add max_length=72 to LoginRequest.password and SetupRequest.master_password
- Update field validator in SetupRequest to explicitly check max_length
- Add comprehensive tests for password length validation (6 new test cases)
- Document the 72-byte limitation in Features.md (master password options)
- Add new section 12 'Password Hashing' in Backend-Development.md explaining:
- The bcrypt truncation behavior
- Why the limit is enforced
- The validation flow from frontend to backend
- What happens when passwords exceed the limit
All existing tests pass, no regressions introduced.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
