icons disappear from cache directory

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Problem description

I tried a few weekly builds for FC1.1. It frequently leads to error messages during startup related to cached icons, e.g.

```
Cannot find icon: /home/xyz/.cache/FreeCAD/Cache/AddonManager/MacroIcons/Macro_3D_Parametric_Curve.png
Cannot find icon: /home/xyz/.cache/FreeCAD/Cache/AddonManager/MacroIcons/Parametric_Curve_FP.svg
Cannot find icon: /home/xyz/.cache/FreeCAD/Cache/AddonManager/MacroIcons/FCTexture.png
Cannot find icon: /home/xyz/.cache/FreeCAD/Cache/AddonManager/MacroIcons/120px-FCBmpImportScreenshot.png
... quite a few more
```

Once I manually copied icons from other places around ~/.local/share/Freecad/Macro/ to this directory, but apparently the cache dir gets emptied from time to time and icons are not reinstalled even after updating the addons. It is however not fully empty, it contains BSpline3D_icon.xpm and Macro_CenterOfMass.svg.
Any idea why this happens or how to prevent it?

Why are the icons copied there, anyway? Isn't is more logical to keep them at the same space as the addon code?

### Full version info

```shell
happened in several weekly builds over the last months

OS: openSUSE Tumbleweed (KDE/plasma6/xcb)
Architecture: x86_64
Version: 1.1.0dev.14555 (Git shallow) AppImage
Build date: 2025/09/12 03:41:38
Build type: Release
Branch: main
Hash: 952bff5b63a62b55a7ea1623edfb39e90dee2d4c
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: C/Default (C)
Navigation Style/Orbit Style/Rotation Mode: Touchpad/Trackball/Drag at cursor
Stylesheet/Theme/QtStyle: unset/FreeCAD Classic/fusion
Logical DPI/Physical DPI/Pixel Ratio: 96/127.628/1
Installed mods:
* Silk 0.2.0
* FeedsAndSpeeds 0.6.0
* kicadStepUpMod 11.7.7
* Assembly4 0.60.2
* fasteners 0.5.42
* offline-documentation 1.0.0-alpha
* MeshRemodel 1.10.38
* LCInterlocking
* parts_library
* 3D_Printing_Tools
* A2plus 0.4.68
* 3DfindIT 1.2.0
* EM 2.1.1
* ExplodedAssembly
* ThreadProfile 1.97.0
* FrameForge-backup-before-zip-migration 0.1.3 (Disabled)
* workfeature
* Lithophane
* FrameForge 0.1.5
* Manipulator 1.6.3
* lattice2 1.0.0
* Defeaturing 1.2.9
* Assembly3 0.12.2
* InventorLoader 1.5.1
* freecad.gears 1.3.0
* CurvedShapes 1.0.13
* Curves 0.6.70
* frame 0.1.1
* FEM_FrontISTR 0.2.0
* fcgear 1.0.0
* Pyramids-and-Polyhedrons
* pyrate
* OpticsWorkbench 1.2.2
* CommandPanel
* CamScripts
```

### Subproject(s) affected?

None

### Anything else?

_No response_

### Code of Conduct

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