Add optional `analyticsEvents?: readonly string[]` to `UseCaseManifest`
in `define-feature.ts` so manifests can declare which analytics events a
use case emits. Field defaults to absent (treated as []) — all existing
manifests remain valid without changes.
Update the feature generator template to emit `analyticsEvents: []` so
newly scaffolded features are analytics-declaration-ready from day one.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>