Translate "Managing State" and unify styles of chapter top pages

[smikitky]

"Managing State" の翻訳です。

あと各章のイントロページのフォーマットにいろいろ不整合が出ているので統一作業も行っています。

[github-actions]

Size changes

📦 Next.js Bundle Analysis for react-dev

This analysis was generated by the Next.js Bundle Analysis action. 🤖

Three Pages Changed Size

The following pages changed size from the code in this PR compared to its base branch:

Page	Size (compressed)	First Load
/404	77.33 KB (🟡 +5 B)	180.49 KB
/500	77.33 KB (🟡 +5 B)	180.48 KB
/[[...markdownPath]]	78.74 KB (🟡 +5 B)	181.9 KB

Details

Only the gzipped size is provided here based on an expert tip.

First Load is the size of the global bundle plus the bundle for the individual page. If a user were to show up to your website and land on a given page, the first load size represents the amount of javascript that user would need to download. If next/link is used, subsequent page loads would only need to download that page's bundle (the number in the "Size" column), since the global bundle has already been downloaded.

Any third party scripts you have added directly to your app using the <script> tag are not accounted for in this analysis

Next to the size is how much the size has increased or decreased compared with the base branch of this PR. If this percentage has increased by 10% or more, there will be a red status indicator applied, indicating that special attention should be given to this.

[koba04]

👍 LGTM!!!