Issue: Update TypeScript Types to Match New Backend Schema

[NahomAlemu]

Description

The backend ERD schema has been redesigned. Frontend TypeScript interfaces in models/activity.ts and models/activityDatabase.ts are now out of sync with the backend entity definitions, causing runtime errors like TypeError: Cannot read properties of undefined (reading 'join').

Tasks

Tasks:

• Update nsc-events-nextjs/models/activity.ts interface
• Update nsc-events-nextjs/models/activityDatabase.ts interface
• Create nsc-events-nextjs/types/media.ts with Media interface
• Create nsc-events-nextjs/types/tag.ts with Tag interface
• Verify no TypeScript compilation errors
• Update related test mocks if needed

Relates to

#142