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/config/settings.py

@@ -25,6 +25,7 @@ DATA_DIR = _config.data_dir
 DISPLAY_TIME_ZONE = _config.default_timezone
 DIRECTORY = _config.directory
 OIDC = _config.oidc
+SMTP = _config.smtp
 
 INSTALLED_APPS = [
     "django.contrib.contenttypes",
@@ -34,6 +35,8 @@ INSTALLED_APPS = [
     "portal.audit",
     "portal.accounts",
     "portal.shell",
+    "portal.mailer",
+    "portal.scheduler",
 ]
 
 MIDDLEWARE = [
@@ -90,6 +93,10 @@ LANGUAGE_CODE = "en"
 LANGUAGES = [("en", "English"), ("de", "Deutsch")]
 LOCALE_PATHS = [BASE_DIR / "portal" / "locale"]
 
+# E-mails use the portal-wide language and form of address (a per-device choice cannot reach
+# server-sent mail). Becomes a runtime setting with the settings registry.
+MAIL_LANGUAGE = "de"
+
 # Static files served by whitenoise; assets are built into the image.
 STATIC_URL = "static/"
 STATIC_ROOT = BASE_DIR / "staticfiles"