Core: Switching between workbenches squishes the larger one

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Problem description

This problem is most apparent when switching between workbenches which have a vastly different number of rows

https://github.com/user-attachments/assets/dd3d9926-60b9-42e1-9fc4-bcc9e68b30b4

### Full version info

```shell
OS: Ubuntu 25.04 (ubuntu:GNOME/ubuntu/wayland)
Architecture: x86_64
Version: 1.1.0dev.14555 (Git shallow) AppImage
Build date: 2025/08/26 20:37:46
Build type: Release
Branch: main
Hash: a5b3a2caac8feb34070415b637b5fbc2a3043a48
Python 3.11.13, Qt 6.8.3, Coin 4.0.3, Vtk 9.3.1, boost 1_86, Eigen3 3.4.0, PySide 6.8.3
shiboken 6.8.3, xerces-c 3.3.0, IfcOpenShell 0.8.2, OCC 7.8.1
Locale: English/United States (en_US)
Navigation Style/Orbit Style/Rotation Mode: Touchpad/Rounded Arcball/Window center
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Dark/
Logical DPI/Physical DPI/Pixel Ratio: 96/143.907/1
Installed mods:
* FusedFilamentDesign 0.25.250
* Telemetry 1.0.2
* fasteners 0.5.41
* freecad.gears 1.3.0
```

### Subproject(s) affected?

Core

### Anything else?

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

No source file or test is identified. Start by reproducing the workbench switch described in the issue, using the attached video and the reported Ubuntu, Qt, and FreeCAD versions, then trace the Core workbench-switching path. Done means switching between workbenches with different row counts no longer squishes the larger one.

Written by the indexing model from the issue text.