Canvas extension issue when using built-in app zoom

### Short summary

Canvas extension offset issue when using built-in app zoom

### Affected version or release

v1.0.24

### Installation context

App installed on MacOS 15.7.7

### What happened?

When a canvas extension is loaded, any zoom change other than default render the app unusable due to the webview of the canvas extension not applying the zoom and getting offset inside the GH app window, see:

### Steps to reproduce

1. Load any canvas extension using the webview
2. zoom in/out in the app using ctrl +/-

### Expected behavior

- canvas extension is also affected by the zoom, and follows the layout as expected

### Additional context

_No response_

macOS 15.7.7 上で v1.0.24 を使用し、webview に canvas 拡張機能を読み込んで Ctrl+/- でアプリのズームを変更して、問題を再現します。canvas 拡張機能の webview におけるズームとレイアウトの処理を調査します。拡張機能がずれたり使用不能になったりせず、アプリのズームに追従すれば完了です。

索引モデルが issue の本文から書いたものです。