04-infrastructure-as-code - [Add TypeScript CDK sample and reorganize CDK folder structure]

I'd like to contribute a new TypeScript CDK sample and reorganize the CDK folder structure to support multiple languages.

Proposed Changes

1. New Sample: knowledge-base-rag-agent (TypeScript CDK)

- Full-stack RAG agent with Amazon Bedrock AgentCore
- Knowledge Base with OpenSearch Serverless for vector storage
- AgentCore Memory (short-term and long-term)
- REST API with Lambda and Cognito authentication
- Next.js web interface with CloudFront distribution
- One-command deployment with comprehensive documentation

2. Folder Reorganization

- Move existing Python CDK samples from cdk/ to cdk/python/
- Add new TypeScript samples under cdk/typescript/
- Update READMEs with language comparison and corrected paths

Start by inspecting the existing Python samples under cdk/ and the repository READMEs to understand their current layout and deployment conventions. Done means adding the knowledge-base-rag-agent TypeScript CDK sample, placing Python and TypeScript samples under their proposed folders, and updating the READMEs with language comparisons and corrected paths.

Written by the indexing model from the issue text.