Feature/donations repository

[pujitakalinadhabhotla]

ℹ️ Issue

Closes DonationsRepository: admin-focused queries and helpers

📝 Description

This PR implements a dedicated repository layer for donations to handle complex database queries, pagination, filtering, and aggregations.

Changes made:

1. Created DonationsRepository class with 5 required methods for data access operations
2. Implemented findPaginated() with flexible filtering (by donation type, amount range, date range, anonymity status, and recurring intervals)
3. Added searchByDonorNameOrEmail() for case-insensitive search across donor name and email fields
4. Built getTotalsByDateRange() to calculate aggregate totals and counts for specific date ranges
5. Implemented findRecentPublic() that returns privacy-aware public donations (r
6. Wrote unit test suite with 20+ test cases covering all methods and edge cases
7. Used TypeORM QueryBuilder for efficient, type-safe database queries

✔️ Verification

1. Run npm test donations.repository.spec.ts to execute the full test suite
2. All 20+ tests should pass
   • Pagination logic with various page sizes and filters
   • Search functionality with multiple field matching
   • Aggregate calculations (sum, count) with null handling
   • Delete operations with error cases
   • Query builder method call verification