Building the renderer on macOS (CauldronGPU.Setup.Platform): Apple's command-line tools
for Swift and Metal, pkg-config and SDL3 from Homebrew, and, for the Vulkan backend
that runs through MoltenVK, Vulkan's loader and headers.
Looks in pkg-config's own search, Homebrew (/opt/homebrew, /usr/local), MacPorts
(/opt/local) and LunarG's SDK (~/VulkanSDK/<version>/macOS). Installs through
Homebrew, and installs Homebrew itself with its official installer when it is missing.