Maintainer Feature authoring

Add a reviewed first-party Feature to client-api.

Feature authoring is an internal maintainer workflow, not a public publishing surface. Add the TypeScript implementation under apps/client-api/src/plugins, register its handler in feature-runtime.ts, and add its manifest to the shared first-party catalog.

Every Feature must declare events, permissions, configuration schema, and failure mode. Add unit tests for allow, ask, block, failure, audit, and UI-visible outcomes as applicable.

export async function runMyFeature(event, config, capabilities) {
  return { decision: "allow", outcomes: [] };
}