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/Services/ImageResolverService.cs

@@ -0,0 +1,42 @@
+using CMSMicroservice.Application.Common.FileManager;
+using CMSMicroservice.Protobuf.Protos.ImageResolver;
+using Grpc.Core;
+
+namespace CMSMicroservice.WebApi.Services;
+
+/// <summary>
+/// سرویس اختصاصی resolve تصاویر — مسیر نسبی را به base64 data-URI تبدیل می‌کند.
+/// FrontOffice از طریق این سرویس تمام تصاویر دینامیک را دریافت می‌کند.
+/// </summary>
+public class ImageResolverService : ImageResolverContract.ImageResolverContractBase
+{
+    private readonly IFileManager _fileManager;
+
+    public ImageResolverService(IFileManager fileManager)
+    {
+        _fileManager = fileManager;
+    }
+
+    public override Task<ResolveImagesResponse> ResolveImages(ResolveImagesRequest request, ServerCallContext context)
+    {
+        var response = new ResolveImagesResponse();
+
+        foreach (var path in request.Paths)
+        {
+            var dataUri = string.Empty;
+
+            if (!string.IsNullOrWhiteSpace(path))
+            {
+                dataUri = _fileManager.ResolveImageUrl(path);
+            }
+
+            response.Images.Add(new ResolvedImage
+            {
+                OriginalPath = path ?? string.Empty,
+                DataUri = dataUri ?? string.Empty
+            });
+        }
+
+        return Task.FromResult(response);
+    }
+}