Initial commit: Howl M365 email management daemon

Full implementation of the Howl email triage system:
- Microsoft Graph API integration with MSAL auth (client-credentials and delegated modes)
- Claude LLM classification via tool use for structured output
- PostgreSQL database with customers, vendors, whitelist, and email_log tables
- Alembic migration for full schema
- APScheduler daemon with graceful shutdown
- Typer CLI (run, dry-run, status commands)
- Business rule classifier with overrides (whitelist protection, low-confidence fallback)
- Action executor (move to folders, flag, escalate with webhook)
- 35 passing unit tests
- README, SETUP, and NEXT_STEPS documentation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

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+.env
+.msal_cache.bin
+__pycache__/
+*.pyc
+*.egg-info/
+dist/
+.venv/
+venv/
+.pytest_cache/
+.coverage
+htmlcov/