fix: add python3 verification for preflight DNS checks in macbook setup script

setup/macbook.sh

@@ -80,6 +80,15 @@ else
   exit 1
 fi
 
+# Verify python3 for preflight DNS checks
+if command -v python3 &>/dev/null; then
+  log_success "python3 found"
+else
+  log_error "python3 not found — required for preflight DNS validation"
+  log_error "Install it with: brew install python"
+  exit 1
+fi
+
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