Add support for Free Mobile SSO authentication by implementing login_cred_mobile which parses the SSO page with BeautifulSoup and exchanges the resulting token for an OQEE access token. Rename login_cred_abo to login_cred_fbx, introduce a self.fbx flag (and mark 8-digit numeric usernames as abo/non-FBX), and update the login selection logic to call the appropriate handler (FBX vs mobile). Also import BeautifulSoup, simplify some request headers, add bs4 to pyproject.toml, and update the lockfile accordingly.
Improved code structure and docstrings in utils/input.py, updated imports for clarity, and enhanced validation error handling. Added pylint to the dev dependency group in pyproject.toml for code quality checks. Removed unused imports from main.py.
