refactor: modularize audit and harden build validation

audit/internal/webui/server_test.go

@@ -1145,6 +1145,10 @@ func TestMissingAuditJSONReturnsNotFound(t *testing.T) {
 
 func TestSupportBundleEndpointReturnsArchive(t *testing.T) {
 	dir := t.TempDir()
+	// Isolate os.TempDir(): BuildSupportBundle stages and writes its archive
+	// there, and a concurrent support-bundle test in another package would
+	// otherwise race on the same paths.
+	t.Setenv("TMPDIR", dir)
 	exportDir := filepath.Join(dir, "export")
 	if err := os.MkdirAll(exportDir, 0755); err != nil {
 		t.Fatal(err)