test: improve app/core test coverage to 100%

Issue Title: Improve unit test coverage for app/core/ modules to 100%

Issue Description:

Summary The app/core/ modules (auth.py, database_triggers.py, logger.py, rbac.py) have insufficient test coverage, with gaps ranging from 81% to 90%. Uncovered paths include error handling branches, optional parameter logic, convenience function delegation, and defensive checks.

Current State

Module	Coverage
auth.py	89%
database_triggers.py	90%
logger.py	81%
rbac.py	87%

Uncovered Code Paths auth.py — Custom token expiry, missing sub claim, invalid UUID parsing, user-not-found in DB database_triggers.py — main entry point not extractable for testing logger.py — 20+ instance methods, all convenience functions, warning method, optional dependency import fallback rbac.py — Invalid role handling, permission rejection branches, require_authentication guard, get_user_role_summary

Acceptance Criteria All four modules reach 100% line coverage