docs(guides): note supported Node version range in Quick Start prerequisites

Author: bgagent

docs/guides/QUICK_START.md

@@ -9,6 +9,7 @@ Install these before you begin:
 - **AWS account** with credentials configured (`aws configure`). If you use named profiles, set `AWS_PROFILE` before running any commands in this guide.
 - **Amazon Bedrock** — The agent invokes Claude through Bedrock. IAM `grantInvoke` in the CDK stack is required but **not sufficient**: your account must also satisfy [Amazon Bedrock model access](https://docs.aws.amazon.com/bedrock/latest/userguide/model-access.html) for the model you use (including Anthropic first-time use where applicable, Marketplace subscription flow on first serverless use, and a valid payment method for Marketplace-backed models). See **Amazon Bedrock before your first task** after Step 3.
 - **Docker** - for building the agent container image
+- **Node.js** v20 or later (Node 24 is the supported maximum — see CI matrix)
 - **mise** - task runner ([install guide](https://mise.jdx.dev/getting-started.html))
 - **AWS CDK CLI** - `npm install -g aws-cdk` (after mise is active)