Closes#45
- New redmine_reporter/mailer.py: SMTP email sending with
{author}/{period} template substitution, MIME attachment
with correct content-type per file extension
- Config.get_email_config(): returns EmailConfig from YAML
or None when not configured
- CLI --send flag: sends report after generation, works with
--output, --commit, or standalone (saves to template path)
- 31 new tests (22 mailer + 6 CLI + 3 config)
- 249/249 tests passing, ruff clean, mypy clean
