Changes:
- Save issue-prefix in config.yaml when using --no-db mode
(previously only saved in database which doesn't exist in no-db mode)
- Add config.ResetForTesting() to allow reloading config in tests
- Simplify test to verify config values rather than execute subsequent
commands (cobra's flag caching makes multi-Execute() testing complex)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>