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/mailer/models.py

@@ -0,0 +1,29 @@
+from django.db import models
+
+
+class OutboxMail(models.Model):
+    """One e-mail waiting to be sent, being sent, sent or failed. Owned by `mailer` (AD-19)."""
+
+    class Status(models.TextChoices):
+        QUEUED = "queued"
+        SENDING = "sending"
+        SENT = "sent"
+        FAILED = "failed"
+
+    template = models.CharField(max_length=100)
+    recipient = models.CharField(max_length=254)
+    subject = models.CharField(max_length=300)
+    # Kept only until the mail is sent: it may hold a one-time link.
+    body_text = models.TextField(blank=True)
+    status = models.CharField(max_length=10, choices=Status.choices, default=Status.QUEUED)
+    attempts = models.PositiveSmallIntegerField(default=0)
+    created_at = models.DateTimeField()
+    next_attempt_at = models.DateTimeField()
+    claimed_at = models.DateTimeField(null=True, blank=True)
+    sent_at = models.DateTimeField(null=True, blank=True)
+    # What went wrong, in words without the recipient or the text of the mail.
+    last_error = models.CharField(max_length=200, blank=True)
+
+    class Meta:
+        indexes = [models.Index(fields=["status", "next_attempt_at"])]
+        ordering = ["id"]