0.5

Native Windows + CUDA builds and packaging hardening carried over from 0.4: the x86_64-pc-windows-msvc build (build.rs Windows branches, static-link delay-load), the Windows release artifact with bundled CUDA/cuDNN/OpenBLAS DLLs, the code-signing decision, and a developer Windows build guide. Tracked by #25 (umbrella) and #58 (feasibility spike + porting plan).