feat: add DynamoDB REST example

[earguinarena]

Summary

• Add a complete API Gateway REST + DynamoDB CDK example with five independent Lambda handlers.
• Configure published lambda-api-decorators packages, named LambdaApiConfig registries, least-privilege DynamoDB grants, and the configured POST handler.
• Add focused documentation, root pytest importlib configuration, and dedicated CI with Docker-backed CDK synthesis.

Validation

• 15 passed, 6 skipped locally.
• Skips are limited to CDK bundling because Docker is inaccessible in the local environment.
• CI requires Docker and rejects skips.
• compileall and git diff --check pass.

Commits

• 2974307 test: define DynamoDB REST example
• 729a22a feat: add DynamoDB REST example
• 81c7bcb test: compare decorator arguments structurally