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

.dockerignore

@@ -0,0 +1,18 @@
+.git
+.gitignore
+.venv
+__pycache__
+*.pyc
+.pytest_cache
+.ruff_cache
+.env
+.env.*
+!.env.example
+_bmad
+_bmad-output
+.agents
+.vscode
+context-resources
+staticfiles
+*.sqlite3*
+skills-lock.json