[Aisoh] [Frontend] Wire Activity Feed to real API data

[aisoh877]

/claim #822

Summary

• replace the homepage ActivityFeed mock timeline with a real /api/activity query
• normalize multiple possible backend payload shapes into a single frontend activity event model
• add 30-second refresh, loading state, empty state, and graceful unavailable state instead of falling back to fake activity
• restore the missing src/lib/animations.ts and src/lib/utils.ts modules so the frontend builds again on current main
• add focused tests for API normalization and the homepage feed states

Verification

• npm test -- --run src/__tests__/activity-api.test.ts src/__tests__/home-activity-feed.test.tsx
• npm run build

Notes

• the feed now shows real events when the API is present, No recent activity when it is empty, and Activity feed unavailable right now. when the endpoint errors
• I kept the change scoped to the homepage feed rather than introducing a larger realtime/event bus refactor