Create Windows x64 build (SDL3 + DXVK + OpenAL + FFMPEG)

[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
• FFMPEG for videos

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:

• Focus on MinGW-w64 toolchain
• This will deprecate both VC6 and WIN32 (MSVC) builds in favour of MinGW-w64, so we assume and accept that will to break compatibility with these build methods.
• Vulkan graphics via DXVK
• OpenAL audio
• 64-bit native (x86_64)

Acceptance Criteria

• CMake preset windows64-deploy created and tested
• DXVK builds and links on Windows (Vulkan requirement documented)
• OpenAL integration working on Windows
• Intro screen and mission briefing videos playing with sound
• Game builds, runs, and reaches main menu
• Skirmish mode playable (determinism preserved)
• Build instructions documented

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

[ebellumat]

I think I've fixed the music playback, I don't know if was an issue on Windows, but at least on Mac OS the music never played for me.

[fbraz3]

I think I've fixed the music playback, I don't know if was an issue on Windows, but at least on Mac OS the music never played for me.

This is a bug introduced in beta 5, can you please cherry pick it into a new pr? Thanks!