build: package universal Windows runtime and verify automatic CPU fallback

.gitignore

@@ -8,6 +8,8 @@ dist/
 __pycache__/
 /apps/desktop/src-tauri/gen/
 /apps/desktop/src-tauri/resources/searchi-gemma-worker*
+/apps/desktop/src-tauri/resources/vulkan-1.dll
+/apps/desktop/src-tauri/resources/VULKAN-LICENSE.txt
 /apps/desktop/src-tauri/resources/embeddinggemma2/
 /apps/desktop/src-tauri/resources/media-runtime/bin/
 /apps/desktop/src-tauri/icons/android/