docs: update references from old linting tools to Ruff

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

.github/instructions/python-backend.instructions.md

@@ -7,13 +7,11 @@ applyTo: "app/**/*.py"
 These instructions apply to all Python code in the `app/` directory.
 
 ## Code Style
-- Use **Black** formatter with 120 character line length
-- Use **isort** with Black profile for import organization
-- Follow **flake8** rules (ignore E203, W503 as per `.pre-commit-config.yaml`)
+- Use **Ruff** for linting and formatting with 120 character line length
 - All functions must have type hints for parameters and return values
 - Use `from typing import Optional, Dict, List, Any, Union` as needed
 
-## Import Order (isort with Black profile)
+## Import Order (Ruff enforces isort-compatible ordering)
 ```python
 # Standard library imports
 import os