Prevent stack deletion unless DynamoDB resources are cleaned up

Issue: Tables are left scaled up after stack deletion. We have banners in the lab explaining the importance of deleting DDB tables, but these aren't foolproof.

Recommended resolution:
- [X] 1. Tables in the hands on python labs are tagged on creation
- [ ] 2. We should create a CFN custom resource or similar that blocks stack deletion if the DDB tables are not cleaned up
- [ ] 3. We should send an error message in the stack events if the tables still exist, and return a hyperlink to AWS resource manager to review the list of tables and clean them up

Start with the hands-on Python lab stack definitions and the existing table-tagging work. Review the CloudFormation custom-resource approach for checking tagged DynamoDB tables during deletion, including how stack events can report failure and link to AWS Resource Manager. Done means deletion is blocked until the tables are cleaned up.

Written by the indexing model from the issue text.