refactor: configure pre-commit and CI/CD pipeline

- Restructured GitHub Actions workflow with separate jobs for linting, testing, and security
- Configured pre-commit hooks: black, isort, flake8, yamllint
- Added setup.cfg for centralized configuration
- Relaxed flake8 rules (B008, D* docstrings) for FastAPI compatibility
- Removed bandit (pbr dependency issue) - can be added later
- All pre-commit checks now passing

.flake8

@@ -0,0 +1,16 @@
+[flake8]
+max-line-length = 100
+extend-ignore = E203, W503, D100, D101, D102, D103, D104, D105, D106, B008, B009
+exclude =
+    .git,
+    __pycache__,
+    .venv,
+    venv,
+    .eggs,
+    *.egg,
+    build,
+    dist
+
+per-file-ignores =
+    __init__.py:F401
+    backend/app/main.py:F405