Techdraw: SectionOrigin position in section plane is not taken into account except to position the plane

### Problem description

I created a page, then a front view, then a section in perspective in up direction.
I wanted to have a view from the side by changing the X or Y in the section SectionOrigin. (In fact to have the same perspective point for different objects, one by one)
This has not effect. Only Z is considered except to slide the section position in the view.

The only workaround is to add small object to keep the global BoundBox:
-the Source of the section is not taken into account, just the view Source
-it is possible to hide unwanted lines in the section but without a clear association with objects

### Workbench affected?

TechDraw

### Steps to reproduce

Just create a cube.
Create a Techdraw page then a View of the cube in X direction.
Then a section in the Z direction.
Change the SectionOrigin X outside the cube to have a side view

### Expected behavior

In perspective, the cube should be seen in perspective from the side, or not centered if not.

### Actual behavior

The object remains seen from the center of remaining of the BounBox after the section.

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

```shell
OS: Linux Mint 22.3 Cinnamon (X-Cinnamon/cinnamon/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: French/France (fr_FR)
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Light/
QPA/File dialog/Color dialog: xcb/via Qt/via Qt
Navigation Style/Orbit Style/Rotation Mode: Gesture/Rounded Arcball/Window center
Logical DPI/Physical DPI/Pixel Ratio: 96/81.5973/1
OpenGL version/vendor/renderer: 4.6 (Compatibility Profile) Mesa 25.2.8-0ubuntu0.24.04.2/Intel/Mesa Intel(R) Graphics (RKL GT1)
```

### Last known good version (optional)

```shell

```

Reproduce the issue in the TechDraw workbench with a cube, page, view, and section, then vary SectionOrigin X and Y outside the cube. Trace how the section's Source, SectionOrigin, and remaining BoundBox determine the perspective view; done means the section origin affects the perspective viewpoint or intentional off-center placement rather than only sliding the section.

Written by the indexing model from the issue text.