NVIDIA/NVENC alpha 1 — Hermes-KMS virtual displays on NVIDIA

Superseded by alpha 3

This build predates the upstream review fixes. Please use
v0.5.0-nvidia-alpha3
instead: same feature set, plus the frame synchronization fixes in the NVENC
capture path (fence wait, DMA-BUF CPU sync, frame validation), proper
mode-switch error handling and a clean-shutdown fix. The full release notes
and install guide moved there.