BIM: Level and Building 'Auto Working Plane' option does not work

### Problem description

I am not completely sure how this functionality should work, but it seems to me it does not work at all.
I think this should be working only when `Set Working Plane` is enabled.

I am able to reproduce in FC 1.1.3

### Workbench affected?

BIM

### Steps to reproduce

- open new file
- create `Arch_Level` obejct
- enable `Auto Working Plane` option of the level in the View properties
- double click the Level in the project tree or BIM Views Manager to activate it

### Expected behavior

The working plane should be set to `Auto`

Note: the behavior should follow the same behavior when deactivating the Level as when this feature is disabled.

### Actual behavior

The working plane is set to `Level`

### Development version About Info (in Safe Mode)

```shell
OS: Debian GNU/Linux 13 (trixie) (GNOME/gnome-xorg/xcb)
Architecture: x86_64
Version: 26.3.0dev.20260804 (Git shallow) AppImage
Build date: 2026/08/04 21:26:11
Build type: Release
Branch: (HEAD detached at 80923ab1b)
Hash: 80923ab1be1f31fff0a54db956177d582a658bab
Python 3.11.14, Qt 6.8.3, Coin 4.0.10 (bundled), Pivy 0.6.11 (bundled), Vtk 9.3.1, boost 1_86, Eigen3 3.4.0, PySide 6.8.3
shiboken 6.8.3, xerces-c 3.3.0, Clipper2 , IfcOpenShell 0.8.0, OCC 7.8.1
Locale: English/Ireland (en_IE)
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Light/
QPA/File dialog/Color dialog: xcb/via Qt/via Qt
Navigation Style/Orbit Style/Rotation Mode: CAD/Rounded Arcball/Window center
Logical DPI/Physical DPI/Pixel Ratio: 96/158.196/1
OpenGL version/vendor/renderer: 4.6 (Compatibility Profile) Mesa 25.0.7-2+deb13u1/Intel/Mesa Intel(R) HD Graphics 4600 (HSW GT2)
```

### Last known good version (optional)

```shell

```

Start by reproducing the issue in the BIM workbench with a new file, an Arch_Level object, and Auto Working Plane enabled. Inspect the Level activation and deactivation behavior alongside the Set Working Plane setting. Done means activating the Level sets the working plane to Auto and deactivation retains the stated behavior when the option is disabled.

Written by the indexing model from the issue text.