Description:
On Windows, Kdenlive version 24.12.3 consistently defaults to 2 threads for rendering in the environment settings, even on multi-core CPUs. The setting appears not to save properly, and performance is limited until the issue is resolved.

Steps to Reproduce:
1. Install Kdenlive on Windows (tested on Windows 11)
2. Open Settings → Configure Kdenlive → Environment
3. Observe the thread count is set to 2, regardless of hardware
4. Manually change it to a higher number (e.g. 15), save
5. Restart Kdenlive
6. Thread count resets to 2

Expected Result:
Thread count should default to a value based on detected CPU threads and remain persistent between sessions.

Observed Result:
Thread count resets to 2 on every startup.

Workaround Discovered:
✅ Reinstall Kdenlive — after the second install, Kdenlive correctly detected and defaulted to 15 threads (on a 16-thread CPU). This suggests the initial config or hardware detection is faulty on first install.

System Info:
- OS: Windows 11 Pro
- Kdenlive Version: 24.12.3
- CPU: Xeon E5-2620 v4 (8 cores / 16 threads)
- RAM: 256 GB DDR4 ECC
- GPU: GTX 1050 Ti

Severity:
⚠️ Moderate — significantly impacts rendering performance on affected systems