Make local GPU detection an injectable package var (localGPU) so the
single-instance path (SetDefaults -> ApplyHardwareDefaults) is deterministically
testable without a real GPU, mirroring the distributed override's coverage.
Adds specs asserting SetDefaults sets the Blackwell physical batch, leaves it
unset on non-Blackwell, and never overrides an explicit batch.
Assisted-by: Claude:opus-4.8 [Claude Code]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>