Fix the shutdown hook and add CI for both examples

[HarshCasper]

The repo had no CI, and both examples were broken on current LocalStack images.

Fixes:

• Init scripts no longer get AWS settings from the image, so the hooks failed with "You must specify a region" and "Unable to locate credentials". All three hooks now default to us-east-1 and the test credentials.
• The shell hooks use set -eo pipefail. Before, init-vpc.sh was reported as SUCCESSFUL even when every command failed.
• Images no longer ship the localstack CLI at /opt/code/localstack/.venv/bin/localstack, so save-pod.sh now exports state through the /_localstack/pods/state endpoint with curl.

Tests:

• example-localstack-cli/test.sh checks init-vpc.sh succeeded, the MyVPC VPC exists, and it has 3 isolated subnets.
• example-docker-compose/test.sh checks the init hooks ran, the secret holds hello-there, and both SSM parameters exist.
• READMEs updated. The import step uses lstk load ./volume/my-pod.zip.
• New workflow with two jobs:
  • lstk: start LocalStack in example-localstack-cli and run its test.
  • compose: start the compose stack, run its test, stop it, check the shutdown hook wrote my-pod.zip, then load it into a fresh LocalStack and check the secret survived.

Verified by CI, since the examples bind the same ports as a running LocalStack.

https://claude.ai/code/session_01DZfDmzUBPqNAu3yFKyfCNM