feat: add scheduler and mail outbox

SMTP adapter with TLS and a fake, outbox with retries, backoff, rate limit and restart safety, scheduler tick with job-run records started by gunicorn, and a send_test_mail command.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N3t4WL7bd9bdHHNjEsxzqC

pyproject.toml

@@ -44,6 +44,10 @@ env = [
     "OIDC_CLIENT_ID=portal-client",
     "OIDC_CLIENT_SECRET=test-only-client-secret",
     "PUBLIC_BASE_URL=https://portal.example.test",
+    "SMTP_HOST=mail.example.test",
+    "SMTP_USERNAME=portal@example.test",
+    "SMTP_PASSWORD=test-only-mail-password",
+    "MAIL_FROM=Portal <portal@example.test>",
 ]
 
 [tool.ruff]