feat: add repository layer with IUnitOfWork and fixed EF base
- ITransaction, IUnitOfWork in DAL.Abstract
- EfTransactionAdapter, EfUnitOfWork<TDbContext>, NotificationUnitOfWork in DAL.EF
- NotificationEfRepository<TEntity>: async-only base, fixed Exists (AnyAsync),
fixed batch Add (AddRangeAsync), single SaveChangesAsync per operation
- TemplateRepository, ProviderRepository, ProviderUsageRepository
- ProviderUsageRepository.IncrementAsync uses atomic PostgreSQL upsert
- ProviderRepository deserializes settings polymorphically via ProviderType discriminator
Ref: IT-628
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Anatolii Grynchuk
4f573da374