[BUG] Application theme does not follow system choice

**Describe the bug**
While the application thankfully does have a dark mode, it defaults to light mode even though my PC is set to use dark mode.
The application should follow the user preference rather than default to light mode; I assumed it only had light mode initially.

**To Reproduce**
Steps to reproduce the behavior:
1. Have windows set to use dark mode
2. Open IoT Explorer
3. Get blinded

**Expected behavior**
It should be in dark mode when launched

**Desktop (please complete the following information):**
- OS: Windows
- OS Version 11
- App version 0.15.8.0

Reproduce the issue by setting Windows 11 to dark mode, launching IoT Explorer version 0.15.8.0, and checking the initial appearance. Trace the application’s theme initialization and system-preference detection, then verify that a launch in dark mode follows the Windows choice while existing light-mode behavior remains available.

Written by the indexing model from the issue text.