Stand up LocalStack as a cheap target for AWS CD primitives

Part of the **Continuous Delivery Vision** ([#8](https://github.com/ChrisonSimtian/Fallout/milestone/8)); tracked under **CD: AWS (LocalStack)** (#15). Sibling of the Azure/Topaz track (#281).

## Idea

Adopt **LocalStack** (de-facto AWS cloud emulator) as a local, free target to build and exercise **AWS-specific CD primitives** without real AWS spend.

## Rough scope (TBD — tracking/scoping issue, not a spec)

- [ ] Confirm LocalStack service coverage for the AWS targets we care about first.
- [ ] Document running LocalStack locally (container) for dev/test.
- [ ] Prototype AWS CD building blocks against it (start narrow — whatever the first real use case needs).
- [ ] Decide what graduates into a Fallout CD primitive vs. stays a sample.
- [ ] Wire LocalStack as an integration-test target once primitives stabilise.

Long-horizon, no release commitment. Start from a concrete use case, not "emulate all of AWS".