change metadata to strings

Author: Kylejeong2

src/stagehandStore.ts

@@ -50,7 +50,7 @@ export const createStagehandInstance = async (
  advancedStealth: config.advancedStealth ?? undefined,
  },
  userMetadata: {
- mcp: true,
+ mcp: "true",
  },
  },
  logger: (logLine) => {