Is codespaces-rails going to be upgraded to Rails 8 and Ruby 3.4?

Current codespaces-rails is for Rails 7.1.3~ and Ruby 3.3.0~ so I suppose the repository should be upgraded to [Rails 8.0.x](https://rubyonrails.org/2024/12/13/Rails-Version-8-0-1-has-been-released) and [Ruby 3.4.x](https://www.ruby-lang.org/en/news/2024/12/25/ruby-3-4-1-released/).

In addition, we can now use the `--devcontainer` option to generate the official devcontainer setup that is available for codespaces as well.

Do you have any plans to upgrade the repository to Rails 8?

該 issue 沒有列出檔案或測試，因此首先定位儲存庫在哪裡宣告 Rails 和 Ruby 的版本，以及其 Codespaces 設定是如何產生的。將目前的設定與 Rails 8.0.x、Ruby 3.4.x 和 --devcontainer 選項進行比較；當儲存庫升級至這些版本並採用預期的 devcontainer 設定時，即視為完成。

由索引模型根據 Issue 內容生成。