Refactor NVIDIA GPU Selection into standalone card on validate page

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

audit/internal/webui/server_test.go

@@ -711,6 +711,8 @@ func TestValidatePageRendersNvidiaTargetedStressCard(t *testing.T) {
 		`controlled NVIDIA DCGM load`,
 		`<code>dcgmi diag targeted_stress</code>`,
 		`NVIDIA GPU Selection`,
+		`All NVIDIA validate tasks use only the GPUs selected here.`,
+		`Select All`,
 		`id="sat-gpu-list"`,
 	} {
 		if !strings.Contains(body, needle) {