feat: rebuild base repository hierarchy, add readme and agents

- replace EfRepository/BaseDbContext/UtcValueConverter with BaseEfRepository and BaseRepository
- add IEfRepository interface hierarchy
- consolidate IEntity into Entity.cs, remove standalone IEntity.cs
- add PagedResult
- adjust all namespaces to HrynCo.DAL.Abstract / HrynCo.DAL.EF
- add README.md with solution overview, versioning rules, class diagram
- add AGENTS.md

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

HrynCo.DAL.EF/Core/EfUnitOfWork.cs

@@ -1,10 +1,10 @@
+namespace HrynCo.DAL.EF.Core;
+
 using HrynCo.DAL.Abstract;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Storage;
 
-namespace HrynCo.DAL.EF.Core;
-
-public abstract class EfUnitOfWork<TDbContext> : IUnitOfWork
+public class EfUnitOfWork<TDbContext> : IUnitOfWork
     where TDbContext : DbContext
 {
     private readonly TDbContext _context;
@@ -15,11 +15,6 @@ public abstract class EfUnitOfWork<TDbContext> : IUnitOfWork
         _context = context;
     }
 
-    public Task SaveChangesAsync(CancellationToken cancellationToken = default)
-    {
-        return _context.SaveChangesAsync(cancellationToken);
-    }
-
     public async Task<ITransaction> BeginTransactionAsync(CancellationToken cancellationToken = default)
     {
         if (_currentTransaction != null)
@@ -27,13 +22,8 @@ public abstract class EfUnitOfWork<TDbContext> : IUnitOfWork
             return _currentTransaction;
         }
 
-        IDbContextTransaction tx = await _context.Database.BeginTransactionAsync(cancellationToken);
-        _currentTransaction = new EfTransactionAdapter(tx);
-        return _currentTransaction;
-    }
-
-    public ITransaction? GetCurrentTransaction()
-    {
+        IDbContextTransaction transaction = await _context.Database.BeginTransactionAsync(cancellationToken);
+        _currentTransaction = new EfTransactionAdapter(transaction);
         return _currentTransaction;
     }
 
@@ -41,6 +31,7 @@ public abstract class EfUnitOfWork<TDbContext> : IUnitOfWork
     {
         ITransaction? existing = GetCurrentTransaction();
         bool ownsTransaction = existing is null;
+
         ITransaction tx = existing ?? await BeginTransactionAsync();
 
         try
@@ -73,6 +64,7 @@ public abstract class EfUnitOfWork<TDbContext> : IUnitOfWork
     {
         ITransaction? existing = GetCurrentTransaction();
         bool ownsTransaction = existing is null;
+
         ITransaction tx = existing ?? await BeginTransactionAsync();
 
         try
@@ -102,4 +94,9 @@ public abstract class EfUnitOfWork<TDbContext> : IUnitOfWork
             }
         }
     }
+
+    public ITransaction? GetCurrentTransaction()
+    {
+        return _currentTransaction;
+    }
 }