- Introduced `pyproject.toml` to centralize backend tool configurations (e.g., Ruff, mypy, coverage, pytest).
- Replaced Black, isort, and Flake8 with Ruff for linting, formatting, and import sorting.
- Updated `requirements.txt` to include Ruff and remove replaced tools.
- Added `Makefile` to streamline development workflows with commands for linting, formatting, type-checking, testing, and cleanup.
- Introduced extensive tests for session cleanup, async session CRUD methods, and concurrent cleanup to ensure reliability and efficiency.
- Enhanced `schemas/users.py` with reusable password strength validation logic.
- Improved error handling in `admin.py` routes by replacing `detail` with `message` for consistency and readability.
