cpp-desktop-v0.20.38-4

Windows ARM64 kit now ships the llamacpp backend (rac_backend_llamacpp.lib), built from feat/windows-arm64-llamacpp at 6400217 (ggml MSVC-ARM fix via llama.cpp fork tag runanywhere-b10453.7). macOS ARM64, Windows x64 and both Linux kits are unchanged from -3.