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>

migrations/script.py.mako

@@ -0,0 +1,28 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from __future__ import annotations
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}