Add bulk create and upsert methods to repository

Added `CreateAsync` for bulk entity creation and `UpsertAsync`
and `UpsertSingleAsync` for upsert operations in `IRepository`
and `Repository`. Improved error handling in `UpdateSingleAsync`
and `DeleteSingleAsync` by throwing `NotFoundException` when no
matching entity is found. Refactored `FindAsync` and `UpdateAsync`
for better readability and performance. Cleaned up formatting in
`DeleteAsync`.

src/core/DigitalData.MessagingService.Application/Common/Interfaces/Repositories/IRepository.cs

@@ -11,6 +11,8 @@ public interface IRepository<TEntity> where TEntity : class
     // CREATE
     Task<TEntity> CreateAsync<TDto>(TDto dto, CancellationToken cancellationToken = default);
 
+    Task<IEnumerable<TEntity>> CreateAsync<TDto>(IEnumerable<TDto> dtos, CancellationToken cancellationToken = default);
+
     // READ
     Task<TEntity?> GetByIdAsync(int id, CancellationToken cancellationToken = default);
     Task<IEnumerable<TEntity>> GetAllAsync(CancellationToken cancellationToken = default);
@@ -20,6 +22,11 @@ public interface IRepository<TEntity> where TEntity : class
     Task<int> CountAsync(Expression<Func<TEntity, bool>>? predicate = null, CancellationToken cancellationToken = default);
     Task<bool> AnyAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
 
+    // UPSERT
+    Task<(TEntity Entity, bool Created)> UpsertAsync<TDto>(Expression<Func<TEntity, bool>> predicate, TDto dto, CancellationToken cancellationToken = default);
+    
+    Task<(TEntity Entity, bool Created)> UpsertSingleAsync<TDto>(Expression<Func<TEntity, bool>> predicate, TDto dto, CancellationToken cancellationToken = default);
+
     // UPDATE
     Task UpdateSingleAsync<TDto>(Expression<Func<TEntity, bool>> predicate, TDto dto, CancellationToken cancellationToken = default);
     Task<int> UpdateAsync<TDto>(Expression<Func<TEntity, bool>> predicate, TDto dto, CancellationToken cancellationToken = default);

src/infrastructure/DigitalData.MessagingService.Infrastructure/Repositories/Repository.cs

@@ -25,6 +25,14 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         return entity;
     }
 
+    public async Task<IEnumerable<TEntity>> CreateAsync<TDto>(IEnumerable<TDto> dtos, CancellationToken cancellationToken = default)
+    {
+        var entities = Mapper.Map<IEnumerable<TEntity>>(dtos);
+        await _dbSet.AddRangeAsync(entities, cancellationToken);
+        await Context.SaveChangesAsync(cancellationToken);
+        return entities;
+    }
+
     // --- READ ---
 
     public async Task<TEntity?> GetByIdAsync(int id, CancellationToken cancellationToken = default)
@@ -84,6 +92,59 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         return await _dbSet.AnyAsync(predicate, cancellationToken);
     }
 
+    // --- UPSERT ---
+
+    /// <summary>
+    /// Upsert: if no record matches the predicate, creates a new entity;
+    /// if one or more match, updates the FIRST match.
+    /// Returns the entity and a flag indicating whether it was created (true) or updated (false).
+    /// Auto-saves changes.
+    /// </summary>
+    public async Task<(TEntity Entity, bool Created)> UpsertAsync<TDto>(
+        Expression<Func<TEntity, bool>> predicate,
+        TDto dto,
+        CancellationToken cancellationToken = default)
+    {
+        var entity = await _dbSet.FirstOrDefaultAsync(predicate, cancellationToken);
+
+        if (entity is null)
+        {
+            entity = Mapper.Map<TEntity>(dto);
+            await _dbSet.AddAsync(entity, cancellationToken);
+            await Context.SaveChangesAsync(cancellationToken);
+            return (entity, true);
+        }
+
+        Mapper.Map(dto, entity);
+        await Context.SaveChangesAsync(cancellationToken);
+        return (entity, false);
+    }
+
+    /// <summary>
+    /// Upsert (single-safe): if no record matches the predicate, creates a new entity;
+    /// if exactly one matches, updates it. Throws InvalidOperationException if 2+ match.
+    /// Auto-saves changes.
+    /// </summary>
+    public async Task<(TEntity Entity, bool Created)> UpsertSingleAsync<TDto>(
+        Expression<Func<TEntity, bool>> predicate,
+        TDto dto,
+        CancellationToken cancellationToken = default)
+    {
+        var entity = await _dbSet.SingleOrDefaultAsync(predicate, cancellationToken);
+
+        if (entity is null)
+        {
+            entity = Mapper.Map<TEntity>(dto);
+            await _dbSet.AddAsync(entity, cancellationToken);
+            await Context.SaveChangesAsync(cancellationToken);
+            return (entity, true);
+        }
+
+        Mapper.Map(dto, entity);
+        await Context.SaveChangesAsync(cancellationToken);
+        return (entity, false);
+    }
+
     // --- UPDATE ---
 
     /// <summary>
@@ -113,12 +174,7 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         CancellationToken cancellationToken = default)
     {
         var entities = await _dbSet.Where(predicate).ToListAsync(cancellationToken);
-
-        foreach (var entity in entities)
-        {
-            Mapper.Map(dto, entity);
-        }
-
+        entities.ForEach(entity => Mapper.Map(dto, entity));
         await Context.SaveChangesAsync(cancellationToken);
         return entities.Count;
     }
@@ -150,7 +206,6 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         CancellationToken cancellationToken = default)
     {
         var entities = await _dbSet.Where(predicate).ToListAsync(cancellationToken);
-
         _dbSet.RemoveRange(entities);
         await Context.SaveChangesAsync(cancellationToken);
         return entities.Count;