fix(encode/windows): resolve NVENC at runtime — AMD/Intel hosts no longer crash at start

The nvenc build linked nvEncodeAPI64.dll's entry points at load time, so a
--features nvenc binary hard-crashed on any box without the NVIDIA driver
(AMD/Intel). Entry points now come from a runtime LoadLibrary table
(encode/windows/nvenc.rs load_api); a missing DLL just falls through the
encoder auto-detect to AMF/QSV/software. The generated import lib and all its
plumbing (gen-nvenc-importlib.ps1, nvenc.def, PUNKTFUNK_NVENC_LIB_DIR,
setup-build-env wiring) are gone.

Live-validated on the RTX 4090 box (NVENC session, 7000+ frames).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/windows/deploy-host.ps1

@@ -35,7 +35,7 @@ Set-Location $repo
 
 # Load the persisted build env (Machine scope) into THIS process, so the build sees it even
 # if this shell was started before setup-build-env.ps1 ran (env is inherited at spawn time).
-foreach ($k in 'PUNKTFUNK_NVENC_LIB_DIR','LIBCLANG_PATH','CMAKE_POLICY_VERSION_MINIMUM') {
+foreach ($k in 'LIBCLANG_PATH','CMAKE_POLICY_VERSION_MINIMUM') {
   $v = [Environment]::GetEnvironmentVariable($k, 'Machine')
   if ($v) { [Environment]::SetEnvironmentVariable($k, $v, 'Process'); Write-Host "env    : $k=$v" }
   else { Write-Warning "env $k not set (run setup-build-env.ps1)" }