Allow customization of colors

Describe the feature or problem you'd like to solve

More granular theme definition to allow users to set colors in a way that suits their needs/preferences.

Proposed solution

As an example, I would like to be able to set a higher contrast background (white on blue) for user prompts, so its very easy to orient yourself to the latest context, when multitasking between many different CLI's. Being able to customize link colors, CLI background colors, text colors, etc, to allow for better readability and scanability.

Ideally there would be a way of extending /theme to support custom themes, defined somewhere in a simple theme file.

Example prompts or workflows

No response

Additional context

No response

まず、既存の /theme エントリーポイントと、現在テーマがどのように定義されているかを確認します。シンプルなカスタムテーマファイルの範囲と、プロンプト、リンク、背景、テキストを含めてサポートする必要がある色のカテゴリを決定します。ユーザーが色を個別に設定できるカスタムテーマを定義して適用できれば完了です。