Zoom does not respect Ctrl key for retaining aspect ratio

まだ誰も着手していません。

## Describe the issue
The tooltip for the pan button widget includes the text "x/y fixes axes, CTRL fixes aspect". Holding down x/y works, but Ctrl does not retain the aspect ratio when zooming with the right mouse button (at least not in Firefox).

## Versions

I'm using the `quay.io/jupyter/scipy-notebook` docker image with image id `36fc325c0178`.
```
$ ( set -x ; python -c "import sys; print('\n',sys.version); import ipympl; print('ipympl version:', ipympl.__version__)" ; jupyter --version ; jupyter nbextension list ; jupyter labextension list )
+ python -c 'import sys; print('\''\n'\'',sys.version); import ipympl; print('\''ipympl version:'\'', ipympl.__version__)'

3.12.11 | packaged by conda-forge | (main, Jun 4 2025, 14:45:31) [GCC 13.3.0]
ipympl version: 0.9.7
+ jupyter --version
Selected Jupyter core packages...
IPython : 9.4.0
ipykernel : 6.29.5
ipywidgets : 8.1.7
jupyter_client : 8.6.3
jupyter_core : 5.8.1
jupyter_server : 2.16.0
jupyterlab : 4.4.4
nbclient : 0.10.2
nbconvert : 7.16.6
nbformat : 5.10.4
notebook : 7.4.4
qtconsole : not installed
traitlets : 5.14.3
+ jupyter nbextension list
usage: jupyter [-h] [--version] [--config-dir] [--data-dir] [--runtime-dir] [--paths] [--json] [--debug] [subcommand]

Jupyter: Interactive Computing

positional arguments:
subcommand the subcommand to launch

options:
-h, --help show this help message and exit
--version show the versions of core jupyter packages and exit
--config-dir show Jupyter config dir
--data-dir show Jupyter data dir
--runtime-dir show Jupyter runtime dir
--paths show all Jupyter paths. Add --json for machine-readable format.
--json output paths as machine-readable json
--debug output debug information about paths

Available subcommands: dejavu events execute kernel kernelspec lab labextension labhub migrate nbclassic nbconvert notebook run server troubleshoot trust

Jupyter command `jupyter-nbextension` not found.
+ jupyter labextension list
JupyterLab v4.4.4
/opt/conda/share/jupyter/labextensions
jupyterlab_pygments v0.3.0 enabled OK (python, jupyterlab_pygments)
nbdime-jupyterlab v3.0.2 enabled OK
jupyter-matplotlib v0.11.7 enabled OK
@jupyter-notebook/lab-extension v7.4.4 enabled OK
@jupyterlab/git v0.51.2 enabled OK (python, jupyterlab-git)
@jupyter-widgets/jupyterlab-manager v5.0.15 enabled OK (python, jupyterlab_widgets)
```

報告された JupyterLab セットアップで、Firefox とマウスの右ボタンを使ってパンボタンのズーム動作を再現し、動作する x/y 修飾キーと Ctrl 修飾キーを比較します。パンボタン widget のブラウザー側の入力処理を追跡します。完了条件は、ズーム中も Ctrl がアスペクト比を維持し、tooltip が正確なままであることです。

索引モデルが issue の本文から書いたものです。