Core: Save button does not grey out or change state after clicking, causing visual confusion

### Problem description

There is a UI/UX issue with the Save button behavior. Currently, when a user clicks the Save button, the icon/button does not change its visual state—it does not grey out, disable, or show any indication that the action has been successfully completed.

This lack of instant visual feedback creates uncertainty. Users are left wondering whether the file was actually saved or if the program missed the click, forcing them to repeatedly click the button just to be sure. This hurts the user experience and breaks standard modern UI conventions.

### Workbench affected?

Part Design

### Steps to reproduce

1. Open any project and make a modification.
2. Click the "Save" button on the toolbar
3. Observe the button's appearance immediately after clicking.
4. Notice that it remains fully active and unchanged, giving no visual feedback that the save operation was executed.

### Expected behavior

The Save button should dynamically change its state to give clear visual feedback. Once clicked (and the file is successfully saved), the button should immediately grey out (become disabled) to indicate that there are currently no unsaved changes. It should only become active again once a new modification is made to the document.

### Actual behavior

The Save button stays visually active and identical at all times, leaving the user in doubt about whether their progress was secured or not.

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

```shell
OS: macOS 15.7.7
Architecture: x86_64
Version: 1.1.0.20260325 (Git shallow)
Build date: 2026/03/25 02:17:53
Build type: Release
Branch: (HEAD detached at 34a971666)
Hash: 34a9716668b1ddeb55b914f1c5be644826bdbbbf
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 0.8.4, OCC 7.8.1
Locale: English/United States (en_US)
Navigation Style/Orbit Style/Rotation Mode: CAD/Turntable/Object center
Stylesheet/Theme/QtStyle: OpenLight.qss/OpenLight/
Logical DPI/Physical DPI/Pixel Ratio: 72/129/2
Installed mods:
* PieMenu 1.12.4
* freecad.gears 1.3.0
* OpenTheme 2025.5.20
* fasteners 0.5.51
* CurvedShapes 1.0.14
* Curves 0.6.71
* Assembly4 0.61.0
```

### Last known good version (optional)

```shell

```