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.Infrastructure/DependencyInjection.cs

@@ -1,5 +1,10 @@
 using DigitalData.EmailProfiler.Application.Common.Interfaces;
 using DigitalData.EmailProfiler.Infrastructure.Messaging;
+using DigitalData.EmailProfiler.Infrastructure.Persistence;
+using DigitalData.EmailProfiler.Infrastructure.Queue;
+using DigitalData.EmailProfiler.Infrastructure.Repositories;
+using DigitalData.EmailProfiler.Infrastructure.Services;
+using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 
@@ -17,16 +22,46 @@ public static class DependencyInjection
         this IServiceCollection services,
         IConfiguration configuration)
     {
-        // Register RabbitMQ configuration
+        // --- Database Context ---
+        services.AddDbContext<EmailProfilerDbContext>(options =>
+            options.UseSqlServer(
+                configuration.GetConnectionString("DefaultConnection"),
+                sqlOptions => sqlOptions.EnableRetryOnFailure()));
+
+        // --- Generic Repository ---
+        services.AddScoped(typeof(IRepository<>), typeof(Repository<>));
+
+        // --- External Services ---
+        // Email Service (using MailKit/MimeKit with OAuth2)
+        services.AddScoped<IEmailService, MailKitEmailService>();
+        
+        // PDF Processing Service (using DevExpress.Pdf)
+        services.AddScoped<IPdfProcessingService, DevExpressPdfProcessingService>();
+        
+        // DMS Service (using windream COM Interop)
+        services.AddScoped<IDmsService, WindreamDmsService>();
+        
+        // Encryption Service (using Data Protection API)
+        services.AddScoped<IEncryptionService, DataProtectionEncryptionService>();
+
+        // --- Email Queue ---
+        services.AddSingleton<IEmailQueue, InMemoryEmailQueue>();
+
+        // --- RabbitMQ Configuration ---
         services.Configure<RabbitMqConfiguration>(
             configuration.GetSection(RabbitMqConfiguration.SectionName));
 
-        // Register RabbitMQ command publisher
+        // --- RabbitMQ Command Publisher ---
         services.AddSingleton<ICommandPublisher, RabbitMqCommandPublisher>();
 
-        // Register RabbitMQ command consumer as hosted service
+        // --- RabbitMQ Command Consumer (Background Service) ---
         services.AddHostedService<RabbitMqCommandConsumer>();
 
+        // --- Data Protection (for encryption) ---
+        services.AddDataProtection();
+            // .PersistKeysToFileSystem(new DirectoryInfo(@"C:\ProgramData\EmailProfiler\Keys"))
+            // .SetApplicationName("EmailProfiler");
+
         return services;
     }
 }