Complete APP.md

A complete app should include identity, runtime targets, entries, capabilities, permissions, knowledge templates, Skill refs, Tool refs, Artifact types, Evals, presentation, compatibility, metadata, and Markdown guidance. Use docs/examples/content-engineering-app/APP.md as the current complete fixture.

Checklist

• Keep declarations machine-readable.
• Keep procedures in Agent Skills.
• Keep facts in Agent Knowledge.
• Keep execution in the host runtime.
• Attach app provenance to projected objects.