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/config/health.py

@@ -0,0 +1,23 @@
+"""Liveness check. Database only; never AD, SMTP or the share (AD-18)."""
+
+import logging
+
+from django.db import connection
+from django.http import JsonResponse
+from django.views.decorators.cache import never_cache
+from django.views.decorators.http import require_GET
+
+logger = logging.getLogger(__name__)
+
+
+@require_GET
+@never_cache
+def healthz(request):
+    try:
+        with connection.cursor() as cursor:
+            cursor.execute("SELECT 1")
+            cursor.fetchone()
+    except Exception as exc:  # noqa: BLE001 - any failure means unavailable
+        logger.error("health check failed", extra={"error_type": type(exc).__name__})
+        return JsonResponse({"status": "unavailable"}, status=503)
+    return JsonResponse({"status": "ok"})