Fix AMD GPU false detection, blackbox deadlock, and NOGPU build bloat

- sat.go: DetectGPUVendor lspci fallback now checks GPU device classes
  ([0300]/[0302]/[0380]) per line instead of scanning the whole output for
  vendor name; AMD EPYC servers have dozens of AMD-branded PCIe entries
  (Root Complex, IOMMU, Host Bridge) that were triggering the old check
- blackbox.go: fix deadlock in finishCycle — it held w.mu while calling
  persistState(), which acquires rt.mu then re-acquires w.mu inside
  persistStateLocked(); now w.mu is released before persistState()
- build.sh: remove NVIDIA-specific overlay files (bee-gpu-burn,
  bee-john-gpu-stress, bee-nccl-gpu-stress, bee-nvidia-recover,
  bee-dcgmproftester-staggered, bee-check-nvswitch,
  nvidia-fabricmanager.service.d/) for non-nvidia build variants
- bee-selfheal: gate NVIDIA recovery on BEE_GPU_VENDOR=nvidia so the
  script does not attempt to restart bee-nvidia.service on NOGPU builds

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

audit/internal/platform/sat.go

@@ -182,9 +182,16 @@ func (s *System) DetectGPUVendor() string {
 		return "amd"
 	}
 	if raw, err := exec.Command("lspci", "-nn").Output(); err == nil {
-		text := strings.ToLower(string(raw))
-		if strings.Contains(text, "advanced micro devices") || strings.Contains(text, "amd/ati") {
-			return "amd"
+		// Only match AMD GPU device classes [0300]=VGA, [0302]=3D controller, [0380]=Display.
+		// AMD CPUs also appear in lspci as "Advanced Micro Devices" (Root Complex, IOMMU, etc.)
+		// so matching vendor alone causes false positives on AMD CPU servers without GPUs.
+		for _, line := range strings.Split(strings.ToLower(string(raw)), "\n") {
+			if !strings.Contains(line, "advanced micro devices") && !strings.Contains(line, "amd/ati") {
+				continue
+			}
+			if strings.Contains(line, "[0300]") || strings.Contains(line, "[0302]") || strings.Contains(line, "[0380]") {
+				return "amd"
+			}
 		}
 	}
 	return ""