Add short_ref.csl file and update .gitignore

This pull request addresses an issue with the Typst version of our template, which requires a short_ref.csl file for proper rendering. Currently, this file is included in the .gitignore for the Quarto version, causing it to be absent from the repository and preventing users from rendering the Typst template correctly. Changes made in this PR: 1. Modified .gitignore to remove the entry for short_ref.csl. 2. Added the short_ref.csl file to the repository. 3. Updated .gitignore to include a new entry: /short_ref.csl Rationale: - The short_ref.csl file is necessary for the Typst version of the template to render correctly. - Quarto generates a short_ref.csl file in the root directory each time it renders, which could potentially lead to unintended file changes. - By adding the file to the repository and then ignoring it in the root directory, we ensure that: a) The Typst version has access to the required file. b) Any locally generated short_ref.csl files from Quarto renders won't pollute the git status. This solution maintains compatibility with both Typst and Quarto versions of the template while preventing unintended file tracking issues.