Registers com.kisani.jarvis.feed.refresh as a BGAppRefreshTask.
On each fire it fetches the latest 40 stories and upserts CachedStory
rows so the SwiftData cache is warm before the user opens the app.
Already-cached rows have signalScore / sourceCount refreshed in-place.
Single ModelContainer owned by JarvisApp and shared via
BackgroundRefreshManager.container to avoid multi-container conflicts.
BG task ID registered in AppDelegate and declared in project.yml.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
