[Feature] Add policy-as-code CI/CD pipeline and schema validation

[imran-siddique]

Problem

Policies are YAML files with no schema validator, test harness, diff tool, or GitHub Action. A bad policy YAML could silently permit dangerous actions.

Proposed Solution

1. JSON Schema for policy YAML files (enables IDE validation)
2. agentos policy test CLI command to validate policies against test scenarios
3. agentos policy diff to compare policy changes
4. Reference GitHub Actions workflow for policy PR validation
5. Pre-commit hook for policy schema validation

Priority

Low effort, high value for production adoption.