Refactor solution structure and add RabbitMQ config

Reorganized the solution structure to align with a layered architecture:
- Replaced `src` folder with `core`, `infrastructure`, and `presentation`.
- Moved projects to their respective folders.
- Added `DigitalData.MessagingService.Publisher.Abstraction` project.
- Removed `DigitalData.MessagingService.Client` project.

Updated project configurations and nesting in the solution file.

Added `appsettings.Secrets.json` with RabbitMQ and email account settings:
- RabbitMQ configuration includes hostname, port, credentials, and queue/exchange details.
- Email configuration includes SMTP server details and credentials.

src/core/DigitalData.MessagingService.Application/Common/Dtos/EmailAccountDto.cs

@@ -0,0 +1,21 @@
+namespace DigitalData.MessagingService.Application.Common.Dtos;
+
+/// <summary>
+/// DTO for EmailAccount query results.
+/// </summary>
+public class EmailAccountDto
+{
+    public string Username { get; set; } = null!;
+
+    public string Password { get; set; } = null!;
+
+    public bool PasswordEncrypted { get; set; } = false;
+
+    public string SmtpServer { get; set; } = null!;
+
+    public int SmtpPort { get; set; }
+
+    public bool SmtpUseSsl { get; set; }
+
+    public bool UseOAuth2 { get; set; }
+}

src/core/DigitalData.MessagingService.Application/Common/Interfaces/ICommandPublisher.cs

@@ -0,0 +1,19 @@
+using MediatR;
+
+namespace DigitalData.MessagingService.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 IBaseRequest - covers both IRequest and IRequest<T>)</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 : IBaseRequest;
+}

src/core/DigitalData.MessagingService.Application/Common/Interfaces/IEmailService.cs

@@ -0,0 +1,16 @@
+namespace DigitalData.MessagingService.Application.Common.Interfaces;
+
+/// <summary>
+/// Email service interface for SMTP operations.
+/// Implementation uses Limilabs Mail.dll for production email sending.
+/// SMTP configuration is injected via IOptions&lt;EmailAccountDto&gt; in appsettings.json.
+/// Throws AuthenticationFailedException when SMTP authentication fails.
+/// </summary>
+public interface IEmailService
+{
+    /// <summary>
+    /// Sends an email using the configured SMTP account.
+    /// SMTP credentials are configured in appsettings.json (EmailAccount section).
+    /// </summary>
+    Task SendEmailAsync(string to, string subject, string body, bool isHtml = true, CancellationToken cancellationToken = default);
+}

src/core/DigitalData.MessagingService.Application/Common/Interfaces/IEncryptionService.cs

@@ -0,0 +1,10 @@
+namespace DigitalData.MessagingService.Application.Common.Interfaces;
+
+/// <summary>
+/// Encryption service interface for password encryption.
+/// </summary>
+public interface IEncryptionService
+{
+    string Encrypt(string plainText);
+    string Decrypt(string cipherText);
+}

src/core/DigitalData.MessagingService.Application/Common/Interfaces/IPdfProcessingService.cs

@@ -0,0 +1,26 @@
+namespace DigitalData.MessagingService.Application.Common.Interfaces;
+
+/// <summary>
+/// PDF processing service interface.
+/// Operates on streams instead of file paths for flexibility.
+/// </summary>
+public interface IPdfProcessingService
+{
+    /// <summary>
+    /// Validates if the provided stream contains a valid PDF document.
+    /// Throws InvalidPdfException if the stream is not a valid PDF.
+    /// </summary>
+    Task<bool> ValidatePdfAsync(Stream pdfStream, CancellationToken cancellationToken = default);
+    
+    /// <summary>
+    /// Extracts embedded files from PDF stream to the specified output directory.
+    /// Returns a list of paths to extracted files.
+    /// </summary>
+    Task<IEnumerable<string>> ExtractEmbeddedFilesAsync(Stream pdfStream, string outputDirectory, CancellationToken cancellationToken = default);
+    
+    /// <summary>
+    /// Gets the page count of the PDF document.
+    /// Throws InvalidPdfException if the stream is not a valid PDF.
+    /// </summary>
+    Task<int> GetPageCountAsync(Stream pdfStream, CancellationToken cancellationToken = default);
+}

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

@@ -0,0 +1,30 @@
+using System.Linq.Expressions;
+
+namespace DigitalData.MessagingService.Application.Common.Interfaces;
+
+/// <summary>
+/// Generic repository interface for CRUD operations.
+/// All operations auto-save changes - NO explicit SaveChangesAsync needed!
+/// </summary>
+public interface IRepository<TEntity> where TEntity : class
+{
+    // CREATE
+    Task<TEntity> CreateAsync<TDto>(TDto dto, CancellationToken cancellationToken = default);
+
+    // READ
+    Task<TEntity?> GetByIdAsync(int id, CancellationToken cancellationToken = default);
+    Task<IEnumerable<TEntity>> GetAllAsync(CancellationToken cancellationToken = default);
+    Task<IEnumerable<TEntity>> FindAsync(Expression<Func<TEntity, bool>> predicate, int? skip = null, int? take = null, CancellationToken cancellationToken = default);
+    Task<TEntity?> FindFirstAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
+    Task<TEntity?> FindSingleAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
+    Task<int> CountAsync(Expression<Func<TEntity, bool>>? predicate = null, CancellationToken cancellationToken = default);
+    Task<bool> AnyAsync(Expression<Func<TEntity, bool>> predicate, 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);
+
+    // DELETE
+    Task DeleteSingleAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
+    Task<int> DeleteAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
+}

src/core/DigitalData.MessagingService.Application/Common/Mappings/EmailMappingProfile.cs

@@ -0,0 +1,19 @@
+using AutoMapper;
+using DigitalData.MessagingService.Application.EmailSending.Commands;
+using DigitalData.MessagingService.Publisher.Abstraction;
+
+namespace DigitalData.MessagingService.Application.Common.Mappings;
+
+/// <summary>
+/// AutoMapper profile for Emails
+/// </summary>
+public class EmailMappingProfile : Profile
+{
+    public EmailMappingProfile()
+    {
+        // SendEmailCommand -> OutgoingEmailEvent
+        CreateMap<SendEmailCommand, OutgoingEmailEvent>()
+            .ForMember(dest => dest.Id, opt => opt.MapFrom(_ => Guid.NewGuid()))
+            .ForMember(dest => dest.QueuedAt, opt => opt.MapFrom(_ => DateTime.Now));
+    }
+}