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/BlogPostImageCQ/Commands/DeleteBlogPostImage/DeleteBlogPostImageCommand.cs

@@ -0,0 +1,8 @@
+using MediatR;
+
+namespace CMSMicroservice.Application.BlogPostImageCQ.Commands.DeleteBlogPostImage;
+
+public class DeleteBlogPostImageCommand : IRequest<Unit>
+{
+    public long Id { get; set; }
+}

src/CMSMicroservice.Application/BlogPostImageCQ/Commands/DeleteBlogPostImage/DeleteBlogPostImageCommandHandler.cs

@@ -0,0 +1,29 @@
+using CMSMicroservice.Application.Common.Exceptions;
+using CMSMicroservice.Application.Common.Interfaces;
+using CMSMicroservice.Domain.Entities.Blog;
+using MediatR;
+
+namespace CMSMicroservice.Application.BlogPostImageCQ.Commands.DeleteBlogPostImage;
+
+public class DeleteBlogPostImageCommandHandler : IRequestHandler<DeleteBlogPostImageCommand, Unit>
+{
+    private readonly IApplicationDbContext _context;
+
+    public DeleteBlogPostImageCommandHandler(IApplicationDbContext context)
+    {
+        _context = context;
+    }
+
+    public async Task<Unit> Handle(DeleteBlogPostImageCommand request, CancellationToken cancellationToken)
+    {
+        var entity = await _context.BlogPostImages.FindAsync(new object[] { request.Id }, cancellationToken);
+        if (entity == null || entity.IsDeleted)
+            throw new NotFoundException(nameof(BlogPostImage), request.Id);
+
+        entity.IsDeleted = true;
+
+        await _context.SaveChangesAsync(cancellationToken);
+
+        return Unit.Value;
+    }
+}