APR Quake 2 Vulkan renderer split

Files:
  vk_local.h
  vk_main.cpp
  vk_instance.cpp
  vk_surface.cpp
  vk_device.cpp
  vk_swapchain.cpp

Replace vk_local.h and vk_main.cpp, and add the four new .cpp files to the ref_vk/Q2 project.
Do NOT keep the old vk_main.cpp content.

Build configuration:
  x64 Debug (or the configuration you have been using)

This refactor preserves the current initialization sequence, but separates instance, surface, device, and swapchain responsibilities.
The swapchain diagnostic code is retained.
