fix(scaffold): avoid prompt capture in install wizard

scaffold/scaffold.go

@@ -346,9 +346,9 @@ prompt() {
 	local answer=""
 
 	if [ -n "$default_value" ]; then
-		printf "%s [%s]: " "$label" "$default_value"
+		printf "%s [%s]: " "$label" "$default_value" >&2
 	else
-		printf "%s: " "$label"
+		printf "%s: " "$label" >&2
 	fi
 
 	if [ -r /dev/tty ]; then

scaffold/scaffold_test.go

@@ -120,6 +120,7 @@ func TestGenerateCreatesRecommendedSkeleton(t *testing.T) {
 		"#!/usr/bin/env bash",
 		`MODULE_PATH="example.com/acme/my-mcp"`,
 		`go install "${MODULE_PATH}/cmd/${BINARY_NAME}@latest"`,
+		`printf "%s [%s]: " "$label" "$default_value" >&2`,
 		"config MCP (Codex)",
 		"config MCP (Claude Desktop)",
 		`"${PROFILE_ENV}=${profile}"`,