`.github` folder in a project is not used in the worktree

### Feature summary

Use the `.github` (and private) folders for projects as well

### What problem are you trying to solve?

The session does not take the `.github` or `github-private` folders into account when creating a worktree of a mutli repo project. I created a helpful canvas in a session which I can find in the `.github` repo, yet when I create a new session I cannot use the canvas.

### Proposed solution

Also use the `.github` or `github-private` folders in the worktree.

### Workflow impact

Especially used for multi-repo projects, misses config and functionality right now, including org level Copilot instructions.

### Installation context

_No response_

### Additional context

Local folder setup:

Copilot App:

Worktree:

まず、複数リポジトリのセッションがどのように worktree を作成し、リポジトリのフォルダーを選択するかを追跡します。.github と github-private がどのように扱われるかを確認してください。これらのフォルダーが worktree に含まれ、新しいセッションでキャンバス、設定、組織レベルの Copilot の指示を利用できるようになれば完了です。

索引モデルが issue の本文から書いたものです。