The README described the deployed architecture and resources but never
documented that the repo itself is a CDK v2 app, leaving cdk.json and
the bin/lib layout unexplained for anyone opening the codebase.
Add a "CDK app" section mapping cdk.json, bin/app.ts, the stack file,
cdk.context.json, and the TypeScript config to their roles, so the
infrastructure-as-code component is discoverable from the README.
