Core: Log document switching to the command line when a document gets focus

### Problem description

We now have this new amazing feature, which allows us to have different contexts for each document being edited.

However, the command line still prints messages sequentially, no matter which file is being edited.
It would be good to also have some sort of separation when another document is being edited.

So, for that matter, a message telling which file is now focused would be good to have.
A split line could also be a good addition

```bash
hh:mm:ss # Empty line
hh:mm:ss Switching to /path/to/document/Document.FCStd # Focused document
```

This way, we can distinguish messages from each document at the command line, too.

### Workbench affected?

Core (App, Gui,...)

### Steps to reproduce

n/a

### Expected behavior

n/a

### Actual behavior

n/a

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

```shell
OS: Ubuntu 25.10 (ubuntu:GNOME/ubuntu/wayland)
Architecture: x86_64
Version: 1.2.0dev.20260318 (Git shallow)
Build date: 2026/03/18 23:42:42
Build type: Release
Branch: grafted,grafted
Hash: 7886ebae105b99f176cddbfc62a106ab06a6d021
Python 3.11.14, 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/Trackball/Drag at cursor
Stylesheet/Theme/QtStyle: OpenDark.qss/OpenDark/
Logical DPI/Physical DPI/Pixel Ratio: 96/144.289/1
```

### Last known good version (optional)

```shell

```

Start in the Core App/Gui document-focus handling and trace where command-line messages are emitted when the focused document changes. Done means the command line clearly separates output and identifies the newly focused document, including its path; add or update coverage if the relevant tests are found.

Written by the indexing model from the issue text.