refactor(infrastructure): Improve service implementations and remove legacy references

**Services Refactored:**
- DevExpressPdfProcessingService: Remove unnecessary try-catch (lines 80-87), add stream position validation
- WindreamDmsService: Mark as [Obsolete] - application now only provides email sending functionality
- MailKitEmailService: Keep MailKit implementation (Limilabs DLL to be added separately)

**Custom Exceptions Added:**
- AuthenticationFailedException: OAuth2/IMAP/SMTP authentication failures
- DmsNotAvailableException: windream COM unavailable
- InvalidPdfException: Invalid PDF stream
- NotFoundException: Entity not found in Repository operations

**Legacy Cleanup:**
- Remove legacy VB.NET projects from solution (EmailProfiler.Common, EmailProfiler.Service)
- Delete legacy/ folder reference
- Clean solution file structure

**Stream Validation:**
- All PDF processing methods now validate stream position (reset to 0 if needed)
- Add CanSeek validation for stream-based operations

**Build Status:** ✅ Successful (0 errors, 15 warnings - all acceptable)

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

@@ -9,9 +9,15 @@ public class EmailAccountDto
     public string AccountName { get; set; } = string.Empty;
     public string ImapServer { get; set; } = string.Empty;
     public int ImapPort { get; set; }
+    public bool ImapUseSsl { get; set; }
     public string SmtpServer { get; set; } = string.Empty;
     public int SmtpPort { get; set; }
+    public bool SmtpUseSsl { get; set; }
     public string Username { get; set; } = string.Empty;
+    public string? EncryptedPassword { get; set; }
     public bool UseOAuth2 { get; set; }
+    public string? TenantId { get; set; }
+    public string? ClientId { get; set; }
+    public string? EncryptedClientSecret { get; set; }
     public bool IsActive { get; set; }
 }

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

@@ -0,0 +1,11 @@
+namespace DigitalData.EmailProfiler.Application.Common.Interfaces;
+
+/// <summary>
+/// DMS service interface for windream integration.
+/// </summary>
+public interface IDmsService
+{
+    Task<string> ImportDocumentAsync(string filePath, string objectType, Dictionary<string, string> metadata, CancellationToken cancellationToken = default);
+    Task<bool> DocumentExistsAsync(string documentId, CancellationToken cancellationToken = default);
+    Task<bool> UpdateMetadataAsync(string documentId, Dictionary<string, string> metadata, CancellationToken cancellationToken = default);
+}

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

@@ -0,0 +1,13 @@
+using DigitalData.EmailProfiler.Domain.Entities;
+
+namespace DigitalData.EmailProfiler.Application.Common.Interfaces;
+
+/// <summary>
+/// Email queue interface for outgoing emails.
+/// </summary>
+public interface IEmailQueue
+{
+    Task EnqueueAsync(EmailOutbox email, CancellationToken cancellationToken = default);
+    Task<EmailOutbox?> DequeueAsync(CancellationToken cancellationToken = default);
+    Task<int> GetQueueDepthAsync(CancellationToken cancellationToken = default);
+}

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

@@ -0,0 +1,16 @@
+using DigitalData.EmailProfiler.Application.Common.Dtos;
+
+namespace DigitalData.EmailProfiler.Application.Common.Interfaces;
+
+/// <summary>
+/// Email service interface for IMAP/SMTP operations.
+/// Implementation uses MailKit.
+/// Throws AuthenticationFailedException when OAuth2/password auth fails.
+/// </summary>
+public interface IEmailService
+{
+    Task<IEnumerable<object>> ReceiveEmailsAsync(EmailAccountDto account, CancellationToken cancellationToken = default);
+    Task SendEmailAsync(EmailAccountDto account, string to, string subject, string body, bool isHtml = true, CancellationToken cancellationToken = default);
+    Task DeleteEmailAsync(EmailAccountDto account, int imapUid, CancellationToken cancellationToken = default);
+    Task<string> GetOAuth2TokenAsync(string tenantId, string clientId, string clientSecret, CancellationToken cancellationToken = default);
+}

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

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

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

@@ -0,0 +1,26 @@
+namespace DigitalData.EmailProfiler.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/DigitalData.EmailProfiler.Application/Common/Interfaces/IRepository.cs

@@ -0,0 +1,30 @@
+using System.Linq.Expressions;
+
+namespace DigitalData.EmailProfiler.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);
+}