feat: initial project scaffold

pyproject.toml (Python 3.12, uv), codex/ package (config, db, models),
infra/ (docker-compose + schema), .env.example, .gitignore, README.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,35 @@
+# Python
+__pycache__/
+*.py[cod]
+*.pyo
+*.pyd
+*.so
+
+# Virtual environments
+.venv/
+venv/
+env/
+
+# Distribution / packaging
+dist/
+build/
+*.egg-info/
+*.egg
+
+# Environment secrets — NEVER commit
+.env
+
+# Type-checker and linter caches
+.mypy_cache/
+.ruff_cache/
+
+# Test caches
+.pytest_cache/
+.coverage
+htmlcov/
+
+# Editor / OS artefacts
+.DS_Store
+.idea/
+.vscode/
+*.swp