Gui: Task boxes have a fixed minimum vertical size that cannot be changed

### Problem description

When opening an object for edition via double-clicking on it on the Tree View, their Task Panel is shown. Often there are different sections organized in task boxes within the Task Panel. These task boxes, at least with overlay enabled (which I think now is the default since 1.0 or 1.1) do not resize to their contents by default: instead of shrinking vertically to fit the size of their widgets, they always have a fixed vertical size, which implies the waste of precious vertical real estate on the Task Panel.

## BIM workbench examples

Wall Task Panel in edit mode. Notice the significant amount of blank space below the "Subtractions" item. This one is particularly visible, as this particular task box is shown on many of the Arch objects (those derived from ArchComponent).

Report Task Panel in edit mode. Notice the unused blank space underneath "New statement". This one in particular makes the Report's Task Panel more difficult to use that it should be: most if its content is obscured and requires scrolling back and forth. The huge "SQL Query" text box in the task box below might be another manifestation of it.

## Part workbench examples

Part_Box Task Panel in edit mode. Notice the unused, blank space in the "Geometric Primitives" task box, below the "Height" label

## Additional notes

@maxwxyz this is https://github.com/FreeCAD/FreeCAD/issues/27075 reported again, as you mentioned there was an error unlocking that issue's comments. Feel free to close https://github.com/FreeCAD/FreeCAD/issues/27075 and its associated discussion

### Workbench affected?

None

### Steps to reproduce

On Part workbench:

1. Switch to Part workbench
1. Create a Part::Box
1. Double click on the newly-created object to activate its Task Panel

On BIM workbench:

1. Switch to BIM workbench
1. Create a Wall, or alternatively a Report
1. Double click on the newly-created object to activate its Task Panel

### Expected behavior

There is no unused blank space on any of the task boxes. They resize to their content.

### Actual behavior

Already by default, the task boxes appear to have a fixed minimum size, regardless of the number of widgets they contain. The task box does not resize (shrink) to fit its contents: the fixed size implies a significant amount of unused vertical real estate.

I've noticed that the apparently fix-sized task boxes do resize if:

1. They are the last task box in the panel
2. The app window's size is reduced enough for them to shrink

But I feel nevertheless the bug still applies: they should not expand to show the massive amount of blank space that they currently display. They should instead resize according to the widgets they have inside.

In other words:

| Expected | Actual |
| --- | --- |
| | |

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

```shell
OS: Ubuntu 22.04.5 LTS (ubuntu:GNOME/ubuntu/wayland)
Architecture: x86_64
Version: 1.2.0dev.45042 (Git)
Build date: 2026/01/13 23:21:18
Build type: Release
Branch: main
Hash: 05b1c67f4242ae03fa92e41fbf88d6b7a576206f
Python 3.10.12, Qt 5.15.3, Coin 4.0.0, Vtk 9.1.0, boost 1_74, Eigen3 3.4.0, PySide 5.15.2
shiboken 5.15.2, SMESH 7.7.1.0, xerces-c 3.2.3, IfcOpenShell 0.8.1.post1, OCC 7.8.1
Navigation Style/Orbit Style/Rotation Mode: Touchpad/Trackball/Drag at cursor
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Light/Fusion
Logical DPI/Physical DPI/Pixel Ratio: 96/159.34/1
Installed mods:
* OpenTheme 2025.5.20
* fasteners 0.5.38
```

### Last known good version (optional)

```shell
This is not a regression, but it might have been made more visible since the introduction of the
overlay system in 1.0.
```