feat: Access Review API - stripped down to access review only

- Simplified Prisma schema to only access review models
- Created PermissionsClient for Graph API permission operations
- Added getAppOnlyGraphToken to TokenManager
- Created comprehensive accessReview router with:
  - Campaign CRUD operations
  - Review items listing
  - Decision submission (retain/remove)
  - Campaign execution for permission removals
  - Scheduled reviews management
- Updated _app.ts to only include access review routes
- Removed all non-access-review routers and services

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: pktikkani