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

compose.yaml

@@ -0,0 +1,21 @@
+services:
+  portal:
+    build: .
+    env_file: .env
+    ports:
+      - "8000:8000"
+    volumes:
+      - data:/data
+      - backups:/backups
+    read_only: true
+    tmpfs:
+      - /tmp
+    cap_drop:
+      - ALL
+    security_opt:
+      - no-new-privileges:true
+    restart: unless-stopped
+
+volumes:
+  data:
+  backups: