Two hardening fixes from the fleet-validation audit.
Blackwell Windows hosts drop windows-cuda attempts that cannot offload
sm_120 instead of leaving them ranked behind the b9360 pin. A cuda-12.4
upstream build loads and passes the functional validator but runs the
model on a slow non-native path (an RTX 5090 measured 7.1 tok/s vs
551.2 on cuda-13.3), so one failed pin download away from that is too
close. The coverage check now also reads manifest SM metadata first, so
published cuda12 app bundles (toolkit 12.8, sm_120 included) stay
selectable and make the pin go dormant correctly.
The fork-release Linux planner no longer appends the linux-cpu bundle
for NVIDIA hosts whose CUDA selection produced nothing; it raises so
the caller walks back to an older release with a usable CUDA line,
mirroring the deliberate ROCm policy. Today's walk-back only works
because partial releases ship no CPU bundle; this keeps it working if
a future partial release does.
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