Fix Windows build process and add Windows asset extraction scripts

- Add missing MSYS2 packages to CI: vulkan-loader, vulkan-headers,
  shaderc, stormlib (both x86-64 and arm64), unicorn (arm64)
- Make vulkan-1.dll copy conditional via find_file (fixes MSYS2 builds)
- Use find_library for wininet/bz2 in asset_extract (graceful fallback)
- Add extract_assets.ps1 and extract_assets.bat for Windows users
- Expand BUILD_INSTRUCTIONS.md with MSYS2, vcpkg, and macOS sections
- Update README.md to reference Windows scripts and platforms

.github/workflows/build.yml

@@ -182,6 +182,11 @@ jobs:
             mingw-w64-clang-aarch64-openssl
             mingw-w64-clang-aarch64-zlib
             mingw-w64-clang-aarch64-ffmpeg
+            mingw-w64-clang-aarch64-unicorn
+            mingw-w64-clang-aarch64-vulkan-loader
+            mingw-w64-clang-aarch64-vulkan-headers
+            mingw-w64-clang-aarch64-shaderc
+            mingw-w64-clang-aarch64-stormlib
             git
 
       - name: Configure
@@ -237,6 +242,10 @@ jobs:
             mingw-w64-x86_64-zlib
             mingw-w64-x86_64-ffmpeg
             mingw-w64-x86_64-unicorn
+            mingw-w64-x86_64-vulkan-loader
+            mingw-w64-x86_64-vulkan-headers
+            mingw-w64-x86_64-shaderc
+            mingw-w64-x86_64-stormlib
             mingw-w64-x86_64-nsis
             git