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

portal/adapters/mail/__init__.py

@@ -0,0 +1,15 @@
+"""Mail adapter: the only code that talks SMTP (AD-1)."""
+
+from .base import Mailer, MailError, MailMessage, MailRejected, MailUnavailable
+from .fake import FakeMailer
+from .smtp import SmtpMailer
+
+__all__ = [
+    "FakeMailer",
+    "MailError",
+    "MailMessage",
+    "MailRejected",
+    "MailUnavailable",
+    "Mailer",
+    "SmtpMailer",
+]