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

manage.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python
+"""Django command-line entry point."""
+
+import os
+import sys
+
+
+def main() -> None:
+    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "portal.config.settings")
+    from django.core.management import execute_from_command_line
+
+    execute_from_command_line(sys.argv)
+
+
+if __name__ == "__main__":
+    main()