feat(examples): provide Cedar policy examples and demos #4990

User Story

As an OpenShell maintainer reviewing #4565, I need the Cedar example policies and demos reviewed separately from the policy engine and runtime integration.

Description

Extract the changes under examples/ from #4565 into a dependent PR based on its branch. Include the example-fixture parity tests and the documentation that points to the Cedar examples. Preserve the existing examples' behavior and keep the base PR buildable.

Context

• Parent implementation: feat(policy): support Cedar as an alternate sandbox policy language #4565
• Cedar feature request: feat(policy): Cedar as a policy language in OpenShell #4411
• Requested by @drew during review of the parent PR.

Definition of Done

• feat(policy): support Cedar as an alternate sandbox policy language #4565 contains the Cedar implementation without the example policy/demo changes.
• A dependent PR contains the example policies, demo changes, fixture parity tests, and corresponding documentation.
• Both stack layers pass the checks appropriate to the split.