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/base.py

@@ -0,0 +1,32 @@
+"""The mail interface the outbox uses (AD-1, AD-11)."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Protocol
+
+
+class MailError(Exception):
+    """Base class. Messages never contain the recipient or the text of the e-mail."""
+
+
+class MailUnavailable(MailError):
+    """The server could not take the message right now; trying again later may work."""
+
+
+class MailRejected(MailError):
+    """The server refused the message for good (for example an unknown recipient)."""
+
+
+@dataclass(frozen=True)
+class MailMessage:
+    sender: str
+    recipient: str
+    subject: str
+    body_text: str
+
+
+class Mailer(Protocol):
+    def send(self, message: MailMessage) -> None:
+        """Hand the message to the mail server, or raise MailUnavailable or MailRejected."""
+        ...