refactor(application): Remove IUnitOfWork, add generic IRepository<T> with AutoMapper

- Remove IUnitOfWork pattern (not needed with auto-save repositories)
- Add generic IRepository<T> with CreateAsync<TDto>, UpdateSingleAsync<TDto>, DeleteSingleAsync
- Add UpdateAsync/DeleteAsync for bulk operations
- Add ICommandPublisher interface for RabbitMQ integration
- Add service interfaces: IEmailService, IPdfProcessingService, IDmsService, IEncryptionService, IEmailQueue
- Configure Application DI with MediatR, AutoMapper, FluentValidation

src/DigitalData.EmailProfiler.Application/Common/Interfaces/ICommandPublisher.cs

@@ -0,0 +1,19 @@
+using MediatR;
+
+namespace DigitalData.EmailProfiler.Application.Common.Interfaces;
+
+/// <summary>
+/// Interface for publishing commands to a message broker (e.g., RabbitMQ)
+/// </summary>
+public interface ICommandPublisher
+{
+    /// <summary>
+    /// Publishes a command to the message broker for asynchronous processing
+    /// </summary>
+    /// <typeparam name="TCommand">The command type (must implement IRequest)</typeparam>
+    /// <param name="command">The command to publish</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>Task representing the publish operation</returns>
+    Task PublishAsync<TCommand>(TCommand command, CancellationToken cancellationToken = default) 
+        where TCommand : IRequest;
+}

src/DigitalData.EmailProfiler.Application/DependencyInjection.cs

@@ -0,0 +1,30 @@
+using System.Reflection;
+using FluentValidation;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DigitalData.EmailProfiler.Application;
+
+/// <summary>
+/// Dependency injection configuration for Application layer.
+/// </summary>
+public static class DependencyInjection
+{
+    public static IServiceCollection AddApplicationServices(this IServiceCollection services)
+    {
+        var assembly = Assembly.GetExecutingAssembly();
+
+        // MediatR - Register all handlers
+        services.AddMediatR(config =>
+        {
+            config.RegisterServicesFromAssembly(assembly);
+        });
+
+        // AutoMapper - Register all profiles
+        services.AddAutoMapper(assembly);
+
+        // FluentValidation - Register all validators
+        services.AddValidatorsFromAssembly(assembly);
+
+        return services;
+    }
+}

src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IRepository.cs

@@ -3,17 +3,58 @@ using System.Linq.Expressions;
 namespace DigitalData.EmailProfiler.Application.Interfaces.Repositories;
 
 /// <summary>
-/// Base repository interface for common CRUD operations.
+/// Base repository interface for common CRUD operations with AutoMapper support.
+/// Changes are automatically saved after each operation - no explicit SaveChanges needed.
 /// </summary>
-/// <typeparam name="T">Entity type</typeparam>
-public interface IRepository<T> where T : class
+/// <typeparam name="TEntity">Entity type</typeparam>
+public interface IRepository<TEntity> where TEntity : class
 {
-    Task<T?> GetByIdAsync(int id, CancellationToken cancellationToken = default);
-    Task<IEnumerable<T>> GetAllAsync(CancellationToken cancellationToken = default);
-    Task<IEnumerable<T>> FindAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default);
-    Task<T> AddAsync(T entity, CancellationToken cancellationToken = default);
-    Task UpdateAsync(T entity, CancellationToken cancellationToken = default);
-    Task DeleteAsync(T entity, CancellationToken cancellationToken = default);
-    Task<bool> ExistsAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default);
-    Task<int> CountAsync(Expression<Func<T, bool>>? predicate = null, CancellationToken cancellationToken = default);
+    // ==================== QUERY OPERATIONS ====================
+    
+    Task<TEntity?> GetByIdAsync(int id, CancellationToken cancellationToken = default);
+    Task<IEnumerable<TEntity>> GetAllAsync(CancellationToken cancellationToken = default);
+    Task<IEnumerable<TEntity>> FindAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
+    Task<TEntity?> FirstOrDefaultAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
+    Task<bool> ExistsAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
+    Task<int> CountAsync(Expression<Func<TEntity, bool>>? predicate = null, CancellationToken cancellationToken = default);
+
+    // ==================== CREATE OPERATIONS ====================
+    
+    /// <summary>
+    /// Create entity from DTO using AutoMapper and save immediately.
+    /// </summary>
+    /// <returns>Created entity with ID populated</returns>
+    Task<TEntity> CreateAsync<TDto>(TDto dto, CancellationToken cancellationToken = default) where TDto : class;
+
+    // ==================== UPDATE OPERATIONS ====================
+    
+    /// <summary>
+    /// Update ALL entities matching expression using DTO via AutoMapper.
+    /// WARNING: This can update multiple records. Use UpdateSingleAsync for single-record updates.
+    /// </summary>
+    /// <returns>Number of entities updated</returns>
+    Task<int> UpdateAsync<TDto>(Expression<Func<TEntity, bool>> predicate, TDto dto, CancellationToken cancellationToken = default) where TDto : class;
+
+    /// <summary>
+    /// Update SINGLE entity matching expression using DTO via AutoMapper.
+    /// SAFETY: Throws exception if zero or multiple entities match the predicate.
+    /// </summary>
+    /// <exception cref="InvalidOperationException">Thrown when zero or multiple entities match</exception>
+    Task UpdateSingleAsync<TDto>(Expression<Func<TEntity, bool>> predicate, TDto dto, CancellationToken cancellationToken = default) where TDto : class;
+
+    // ==================== DELETE OPERATIONS ====================
+    
+    /// <summary>
+    /// Delete ALL entities matching expression.
+    /// WARNING: This can delete multiple records. Use DeleteSingleAsync for single-record deletes.
+    /// </summary>
+    /// <returns>Number of entities deleted</returns>
+    Task<int> DeleteAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Delete SINGLE entity matching expression.
+    /// SAFETY: Throws exception if zero or multiple entities match the predicate.
+    /// </summary>
+    /// <exception cref="InvalidOperationException">Thrown when zero or multiple entities match</exception>
+    Task DeleteSingleAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
 }

src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IUnitOfWork.cs

@@ -1,33 +0,0 @@
-namespace DigitalData.EmailProfiler.Application.Interfaces.Repositories;
-
-/// <summary>
-/// Unit of Work pattern for transaction management.
-/// </summary>
-public interface IUnitOfWork : IDisposable
-{
-    IEmailAccountRepository EmailAccounts { get; }
-    IEmailProfileRepository EmailProfiles { get; }
-    IEmailProcessRepository EmailProcesses { get; }
-    IEmailHistoryRepository EmailHistories { get; }
-    IEmailOutboxRepository EmailOutbox { get; }
-
-    /// <summary>
-    /// Save all changes to the database.
-    /// </summary>
-    Task<int> SaveChangesAsync(CancellationToken cancellationToken = default);
-
-    /// <summary>
-    /// Begin a database transaction.
-    /// </summary>
-    Task BeginTransactionAsync(CancellationToken cancellationToken = default);
-
-    /// <summary>
-    /// Commit the current transaction.
-    /// </summary>
-    Task CommitTransactionAsync(CancellationToken cancellationToken = default);
-
-    /// <summary>
-    /// Rollback the current transaction.
-    /// </summary>
-    Task RollbackTransactionAsync(CancellationToken cancellationToken = default);
-}