feat: Pre-commit hooks for plugin manifest validation

[imran-siddique]

Summary

Extend the existing .pre-commit-hooks.yaml to include a hook for plugin manifest validation, so plugin authors get governance feedback locally before pushing.

Motivation

The toolkit already has a .pre-commit-hooks.yaml file, but it does not cover plugin manifest validation. In a marketplace like the Agency Playground where dozens of authors contribute plugins via PRs, catching issues at pre-commit time (before CI) drastically reduces feedback loops and wasted CI cycles.

Plugin authors should know immediately if their manifest:

• Declares blocked tools or MCP servers
• Is missing required capability declarations
• Fails schema validation
• Would be rejected by marketplace policy

Acceptance Criteria

• New pre-commit hook: validate-plugin-manifest
  • Runs agent-marketplace verify on changed plugin.json files
  • Configurable: schema format (copilot-plugin, claude-plugin, generic)
• New pre-commit hook: evaluate-plugin-policy
  • Runs agent-governance evaluate on changed plugin manifests against a local policy file
  • Configurable: policy file path
• Documentation showing how to add these hooks to a plugin marketplace repo
• Example .pre-commit-config.yaml for marketplace repos

Context

Low-effort, high-signal improvement for the Agency Playground governance integration. Shifts feedback left to author time.