Tracking issue: Resolve EditorConfig lint errors

The purpose of this issue is to track tasks related to the effort to resolve violations of our EditorConfig as flagged by [editorconfig-checker](https://github.com/editorconfig-checker/editorconfig-checker).

Start by running editorconfig-checker and reviewing the violations it reports. Identify the tracked tasks from those results, then resolve the applicable EditorConfig violations and rerun the checker until no violations remain.

索引モデルが issue の本文から書いたものです。