Generate API-shaped Harness YAML and load it for deployment

[aidandaly24]

Requested Change

Change the generated harness.yaml to the reviewed API-shaped layout and verify that a generated project deploys.

Scope

• Update YAML generation and the existing file readers.
• The readers accept only the new YAML shape; no backward compatibility with flat YAML is required.
• Keep existing CLI options, wizard behavior, export logic, CDK construct inputs, and IAM behavior unchanged except where directly required to read the generated file.
• Reuse existing validation and update affected tests/examples in place. Do not perform a broad internal schema migration or unrelated cleanup.

Companion PRs: #2436 and aws/agentcore-l3-cdk-constructs#411, both targeting refactor.

Live validation succeeded with the built CLI and locally packaged CDK: create, deploy, READY Harness, and successful invocation. The CLI still needs the compatible CDK release published and pinned before shipping.