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.WebApi/Program.cs

@@ -65,6 +65,7 @@ builder.Services.AddGrpc(options =>
     options.Interceptors.Add<LoggingBehaviour>();
     options.Interceptors.Add<PerformanceBehaviour>();
     options.Interceptors.Add<CMSMicroservice.WebApi.Interceptors.PermissionInterceptor>();
+    options.Interceptors.Add<CMSMicroservice.WebApi.Interceptors.ImagePathResolverInterceptor>();
     //options.Interceptors.Add<ExceptionHandlingBehaviour>();
     options.EnableDetailedErrors = true;
     options.MaxReceiveMessageSize = 1000 * 1024 * 1024; // 1 GB
@@ -92,6 +93,13 @@ builder.Services.AddHealthChecks()
 // Add Controllers for REST APIs
 builder.Services.AddControllers();
 
+// HttpClient for FMS fallback image download
+builder.Services.AddHttpClient("FMS", client =>
+{
+    client.Timeout = TimeSpan.FromSeconds(30);
+    client.DefaultRequestHeaders.Add("User-Agent", "FourSat-CMS/1.0");
+});
+
 #region Configure Cors
 
 builder.Services.AddCors(options =>