GUI crashes on startup on Windows 11 (Qt6Gui.dll, c0000005, Fixedsys font)

### Sanity checks

- [x] I have done the sanity checks, and my issue persists
- [x] These sanity checks are not relevant to the bug

### Deskflow version info

Title: GUI crashes on startup on Windows 11 (Qt6Gui.dll, c0000005, Fixedsys font)

Body:

On Windows 11 hosts that don't have the legacy raster font fixedsys.fon installed, the GUI crashes shortly after launch.

Environment
- Deskflow master (CI build, Qt 6.10.2, windows-2022-x64)
- Windows 11 26100 x64

Symptom

Main window appears for 0–7 seconds, then process exits with 0xC0000005.

WER:
Faulting application: deskflow.exe
Faulting module: Qt6Gui.dll 6.10.2.0
Exception code: 0xc0000005

stderr right before the crash:
DirectWrite: CreateFontFaceFromHDC() failed (Indicates an error in an input file such as a font file.)
for QFontDef(Family="Fixedsys", ... pixelsize=16, styleHint=7 ...)
LOGFONT("Fixedsys", lfWidth=0, lfHeight=-16) dpi=96

Reproduce
1. Install the current CI MSI on a Windows 11 host with no fixedsys.fon in C:\Windows\Fonts.
2. Run deskflow.exe.

### Build type

Local developer build (built it myself)

### Operating systems (OS)

- [x] Windows
- [ ] macOS
- [ ] Linux (X11)
- [ ] Linux (Wayland)
- [ ] BSD-derived
- [ ] Other (please specify)

### Deskflow configuration

windows 11 server
windows 11 client

### What steps will reproduce the problem?

start exe

### Log output

```shell

```

### Additional information

_No response_