add Confidential Computing readiness check + collect nvidia-smi conf-compute -q

New read-only "Check" step reports whether this server can run NVIDIA
Confidential Computing: CPU TEE support (Intel TDX / AMD SEV-SNP, via
dmesg and kvm_amd sysfs params) and GPU firmware CC capability (via
`nvidia-smi conf-compute -q`). Also collect that command's output into
the techdump export bundle.

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

audit/internal/app/app_test.go

@@ -243,6 +243,10 @@ func (f fakeSAT) RunStorageAcceptancePack(_ context.Context, baseDir string, _ b
 	return f.runStorageFn(baseDir)
 }
 
+func (f fakeSAT) RunConfidentialComputingCheckPack(_ context.Context, baseDir string, _ func(string)) (string, error) {
+	return "", nil
+}
+
 func (f fakeSAT) RunCPUAcceptancePack(_ context.Context, baseDir string, durationSec int, _ func(string)) (string, error) {
 	if f.runCPUFn != nil {
 		return f.runCPUFn(baseDir, durationSec)