feat: add Django project scaffold, configuration and container

Environment-variable configuration that fails fast, database-only health
check, JSON request logs with a request id, security headers with a strict
CSP, and a multi-stage non-root Docker image with compose file. Ticket 1.1.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Sk72AxLwQnYttF6VFSxQLt

portal/tests/test_health.py

@@ -0,0 +1,20 @@
+from unittest import mock
+
+import pytest
+from django.db.utils import OperationalError
+
+
+@pytest.mark.django_db
+def test_health_ok(client):
+    response = client.get("/healthz")
+    assert response.status_code == 200
+    assert response.json() == {"status": "ok"}
+
+
+def test_health_down_when_database_unreachable(client, caplog):
+    with mock.patch("portal.config.health.connection") as connection:
+        connection.cursor.side_effect = OperationalError("unable to open database file")
+        response = client.get("/healthz")
+    assert response.status_code == 503
+    assert response.json() == {"status": "unavailable"}
+    assert "unable to open" not in caplog.text