install.ps1 kept detecting arch=amd64 on windows-11-arm because it runs under x64
emulation, where neither $env:PROCESSOR_ARCHITECTURE nor .NET OSArchitecture (on
Windows PowerShell 5.1) reports the real Arm64. Add a CBM_ARCH env override to
install.ps1 (wins over auto-detect; also a genuine escape hatch for emulated
invocations) and have smoke Phase 13 pass the authoritative DL_ARCH. Deterministic
-- no reliance on in-process detection under emulation. Same emulated-arch class
as #907 (uname) and #908.
Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>