feat: integrate PYMS payment gateway, add blog/sitepage/image services, local file manager

Payment Gateway:
- Add PYMSPaymentService: IPaymentGatewayService via gRPC to PYMS microservice
- Add ZarinPalPaymentService: direct ZarinPal integration (backup)
- Register 'pyms' payment provider in DI ConfigureServices
- Add PYMS proto files (pyms_transaction.proto, pyms_public_messages.proto)
- Fix VerifyDiscountWalletCharge: pass 'OK' as status instead of Authority
- Update appsettings: PaymentProvider=pyms, sandbox mode, merchant ID

Blog System:
- Add BlogCategory, BlogPost, BlogPostImage entities and CQRS
- Add proto files and gRPC services for blog management
- Add Mapster profiles for blog responses

Content Management:
- Add SitePage entity and CQRS for static pages
- Add proto and gRPC service for site pages

Image/File Management:
- Add LocalFileManager with disk storage + base64 serving + FMS fallback
- Add ImagePathResolverInterceptor for gRPC responses
- Add ImageResolverService for explicit image resolution
- Add UploadsController for public file serving with FMS fallback
- Add PaymentCallbackController for discount order payment callbacks

Database:
- Add blog and content entity migrations
- Remove ImagePath MaxLength constraints
- Remove old FileManagementService (replaced by LocalFileManager)

src/CMSMicroservice.Application/Common/Behaviours/UnhandledExceptionBehaviour.cs

@@ -22,8 +22,11 @@ public class UnhandledExceptionBehaviour<TRequest, TResponse> : IPipelineBehavio
         catch (Exception ex)
         {
             var requestName = typeof(TRequest).Name;
+            var safeLog = request?.ToString() ?? "";
+            if (safeLog.Length > 2000)
+                safeLog = safeLog[..2000] + "... [TRUNCATED]";
 
-            _logger.LogError(ex, "Request: Unhandled Exception for Request {Name} {@Request}", requestName, request);
+            _logger.LogError(ex, "Request: Unhandled Exception for Request {Name} {Request}", requestName, safeLog);
 
             throw;
         }