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

.env.example

@@ -0,0 +1,24 @@
+# Copy to .env and edit. Never commit .env.
+
+# Required. At least 32 random characters.
+# Generate: python -c "import secrets; print(secrets.token_urlsafe(64))"
+SECRET_KEY=
+
+# Required. Comma-separated host names the portal answers to.
+ALLOWED_HOSTS=portal.example.test
+
+# Optional. Directory for the database. Default /data (the container volume).
+# DATA_DIR=/data
+
+# Optional. true or false. Default false. Never true in production.
+# DEBUG=false
+
+# Optional. Comma-separated IP addresses or networks of reverse proxies. Default empty.
+# Reserved for the client-IP rule in a later entry; currently has no effect.
+# TRUSTED_PROXIES=
+
+# Optional. DEBUG, INFO, WARNING, ERROR or CRITICAL. Default INFO.
+# LOG_LEVEL=INFO
+
+# Optional. IANA time zone used for display. Default Europe/Berlin.
+# DEFAULT_TIMEZONE=Europe/Berlin