Create Windows x64 build (SDL3 + DXVK + OpenAL)

[fbraz3]

Context

Linux (GeneralsXZH) and macOS (GeneralsXZH) both have working cross-platform builds using:

• SDL3 for windowing/input
• DXVK for DirectX 8 to Vulkan graphics translation
• OpenAL for audio

Windows currently only has legacy builds (VC6 32-bit + DirectX 8 + Miles, MSVC 2022 experimental).

Goal

Create a modern Windows x64 build that uses the same unified codebase as Linux/macOS:

• MSVC 2022 or MinGW-w64 toolchain
• Vulkan graphics via DXVK
• OpenAL audio
• 64-bit native (x86_64)
• Maintain coexistence with legacy VC6/win32 presets

Acceptance Criteria

• CMake preset windows64-deploy created and tested
• DXVK builds and links on Windows (Vulkan requirement documented)
• OpenAL integration working on Windows
• Game builds, runs, and reaches main menu
• Skirmish mode playable (determinism preserved)
• Build instructions documented
• Legacy VC6/win32 presets remain unbroken

Notes

• Vulkan must be available on Windows (check driver support)
• DXVK is already proven on Windows via existing reference builds
• This enables single-codebase release for Windows