Set up initial Sphinx documentation and add Normalize filter docstrings

[JaylenTyler]

This PR introduces the initial Sphinx documentation structure under the docs/ directory and sets up basic configuration for project-wide documentation. It includes:

• A functional conf.py with autodoc, napoleon, and viewcode extensions enabled
• An index.rst and modules.rst file to serve as a starting point for documentation
• Updates to pyproject.toml to include Sphinx under optional dev dependencies
• Minimal but complete docstrings added to src/scarr/filters/normalize.py

This work aligns with the feedback provided in response to the original glossary proposal and fulfills the first step toward integrating full project documentation, as discussed in issue #26.

Let me know if you'd prefer a different layout or have other best practices to follow. Thanks for the opportunity to contribute!