fix: tray main-thread message loop, numpy <2.0 pin, installer config copy

- Rewrite tray to run on main thread (pystray owns message loop, uvicorn
  in background thread) — fixes unresponsive confirmation dialogs
- Use native Windows MessageBoxW instead of tkinter (embedded Python
  has no tkinter)
- Pin numpy <2.0 to fix soundcard's numpy.fromstring (removed in 2.0)
- Strip transitive numpy 2.x wheels in build script
- Installer copies config.example.yaml as config.yaml on fresh install
- Suppress noisy screen_brightness_control warnings

pyproject.toml

@@ -46,7 +46,7 @@ windows = [
 ]
 visualizer = [
     "soundcard>=0.4.0",
-    "numpy>=1.24.0",
+    "numpy>=1.24.0,<2.0",
 ]
 dev = [
     "pytest>=7.0",