feat: Add security hardening, agentic coding infrastructure, and test framework

- Add SECRET_KEY and ENCRYPTION_KEY validation on startup
- Implement security headers middleware (X-Frame-Options, CSP, HSTS)
- Add CSRF protection middleware
- Create comprehensive GitHub issue templates and PR template
- Add Makefile with common development tasks
- Configure pre-commit hooks (black, ruff, mypy, bandit, detect-secrets)
- Create docs/CODING_PATTERNS.md with best practices
- Create docs/ERRORS.md documenting all error codes
- Add Architecture Decision Records (ADR) for Celery and Fernet encryption
- Create CHANGELOG.md for version tracking
- Set up pytest test infrastructure with fixtures and factories
- Add sample unit tests for security and config validation
- Create CI/CD workflows (test, lint, security)
- Add comprehensive TODO.md with milestones and progress tracking

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

backend/pytest.ini

@@ -0,0 +1,35 @@
+[pytest]
+asyncio_mode = auto
+testpaths = tests
+python_files = test_*.py
+python_classes = Test*
+python_functions = test_*
+addopts =
+    -v
+    --strict-markers
+    --tb=short
+    --cov=app
+    --cov-report=term-missing
+    --cov-report=html
+    --cov-branch
+markers =
+    unit: Unit tests
+    integration: Integration tests
+    e2e: End-to-end tests
+    slow: Slow running tests
+
+[coverage:run]
+source = app
+omit =
+    */tests/*
+    */migrations/*
+    */__pycache__/*
+    */venv/*
+
+[coverage:report]
+precision = 2
+show_missing = True
+skip_covered = False
+
+[coverage:html]
+directory = htmlcov