Improving the Next.js Example

[kurosakishigure]

Example Description

We need to provide a complete Next.js environment so that users can simply clone the project and run pnpm i + katharsis to get started. Additionally, we should improve the related documentation and simplify the files as much as possible.

Rationale

The files in the example are not complete, and we shouldn't assume that users will have these files already. Instead, we should guide users on how to properly configure the necessary files.

Additional Information

1. We can create a Next.js project using create-next-app, then write the required files and include instructions in the README.md on how to run the project and configure the necessary settings.
2. We also need to add a unit test and a CI test for the example to ensure it works correctly. Additionally, we should exclude the corresponding build directories when committing to Git.
3. We need to update the dependabot.yml file to ensure dependencies in the examples are kept up to date and to verify their compatibility with the latest versions.