feat(application): add DTOs and application layer dependencies

DTOs:
- EmailProfileDto: Profile data transfer object
- EmailAccountDto: Email account data transfer object
- EmailHistoryDto: Email history data transfer object
- EmailAttachmentDto: Attachment data transfer object

Dependencies:
- MediatR 14.2.0 for CQRS (Commands/Queries)
- AutoMapper 12.0.1 for entity-DTO mapping
- FluentValidation 12.1.1 for input validation

This provides the foundation for the application layer implementation.

src/DigitalData.EmailProfiler.Application/Common/Dtos/CommonDtos.cs

@@ -0,0 +1,54 @@
+namespace DigitalData.EmailProfiler.Application.Common.Dtos;
+
+public class EmailProfileDto
+{
+    public int Id { get; set; }
+    public string ProfileName { get; set; } = string.Empty;
+    public int EmailAccountId { get; set; }
+    public string? EmailAccountName { get; set; }
+    public int? ProcessId { get; set; }
+    public string? ProcessName { get; set; }
+    public int PollIntervalMinutes { get; set; }
+    public DateTime? LastPollTime { get; set; }
+    public bool IsActive { get; set; }
+    public string? Comment { get; set; }
+}
+
+public class EmailAccountDto
+{
+    public int Id { get; set; }
+    public string AccountName { get; set; } = string.Empty;
+    public string ImapServer { get; set; } = string.Empty;
+    public int ImapPort { get; set; }
+    public string SmtpServer { get; set; } = string.Empty;
+    public int SmtpPort { get; set; }
+    public string Username { get; set; } = string.Empty;
+    public bool UseOAuth2 { get; set; }
+    public bool IsActive { get; set; }
+}
+
+public class EmailHistoryDto
+{
+    public int Id { get; set; }
+    public int? ProfileId { get; set; }
+    public string? ProfileName { get; set; }
+    public string? SenderAddress { get; set; }
+    public string? Subject { get; set; }
+    public DateTime? EmailDate { get; set; }
+    public DateTime? ProcessedDate { get; set; }
+    public string? Status { get; set; }
+    public int? ErrorCodeValue { get; set; }
+    public string? ErrorMessage { get; set; }
+    public List<EmailAttachmentDto> Attachments { get; set; } = new();
+}
+
+public class EmailAttachmentDto
+{
+    public int Id { get; set; }
+    public string OriginalFileName { get; set; } = string.Empty;
+    public string FilePath { get; set; } = string.Empty;
+    public long FileSize { get; set; }
+    public bool IsEmbeddedFile { get; set; }
+    public string? Status { get; set; }
+    public string? ValidationErrorMessage { get; set; }
+}

src/DigitalData.EmailProfiler.Application/DigitalData.EmailProfiler.Application.csproj

@@ -10,4 +10,10 @@
     <ProjectReference Include="..\DigitalData.EmailProfiler.Domain\DigitalData.EmailProfiler.Domain.csproj" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="AutoMapper.Extensions.Microsoft.DependencyInjection" Version="12.0.1" />
+    <PackageReference Include="FluentValidation.DependencyInjectionExtensions" Version="12.1.1" />
+    <PackageReference Include="MediatR" Version="14.2.0" />
+  </ItemGroup>
+
 </Project>