feat: add admin dashboard, moderation, and transaction monitoring APIs

[Ibinola]

Motivation

• Provide admin-facing APIs to manage users, moderate properties, and monitor transactions via a dedicated AdminModule and secure endpoints.
• Standardize DTOs and enums used by admin queries to avoid ad-hoc string usage and improve type-safety.

Description

• Added src/admin with admin.module.ts, admin.controller.ts, admin.service.ts, and dto/admin.dto.ts implementing endpoints for dashboard stats, user management, property moderation (approve/reject/flag/bulk), and transaction monitoring.
• Registered AdminModule in src/app.module.ts and extended src/types/prisma.types.ts with PropertyStatus, TransactionType, and TransactionStatus enums used by the new DTOs and service.
• Endpoints added include /admin/dashboard, /admin/users, /admin/users/:id (patch), block/unblock routes, moderation queue and actions, and /admin/transactions/monitoring plus summary.
• Closes Create Admin Dashboard #405
• Closes Implement User Management Panel #406
• Closes Add Property Moderation #407
• Closes Implement Transaction Monitoring #408

Testing

• Ran npm run build and the project built successfully (build completed without errors).

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