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/AddBlogPostImage/AddBlogPostImageCommand.cs

@@ -0,0 +1,13 @@
+using MediatR;
+
+namespace CMSMicroservice.Application.BlogPostImageCQ.Commands.AddBlogPostImage;
+
+public class AddBlogPostImageCommand : IRequest<long>
+{
+    public long BlogPostId { get; set; }
+    public string ImagePath { get; set; } = default!;
+    public string ThumbnailPath { get; set; } = default!;
+    public string? AltText { get; set; }
+    public string? Caption { get; set; }
+    public int SortOrder { get; set; }
+}

src/CMSMicroservice.Application/BlogPostImageCQ/Commands/AddBlogPostImage/AddBlogPostImageCommandHandler.cs

@@ -0,0 +1,39 @@
+using CMSMicroservice.Application.Common.Exceptions;
+using CMSMicroservice.Application.Common.Interfaces;
+using CMSMicroservice.Domain.Entities.Blog;
+using MediatR;
+using Microsoft.EntityFrameworkCore;
+
+namespace CMSMicroservice.Application.BlogPostImageCQ.Commands.AddBlogPostImage;
+
+public class AddBlogPostImageCommandHandler : IRequestHandler<AddBlogPostImageCommand, long>
+{
+    private readonly IApplicationDbContext _context;
+
+    public AddBlogPostImageCommandHandler(IApplicationDbContext context)
+    {
+        _context = context;
+    }
+
+    public async Task<long> Handle(AddBlogPostImageCommand request, CancellationToken cancellationToken)
+    {
+        var blogPost = await _context.BlogPosts.FirstOrDefaultAsync(x => x.Id == request.BlogPostId && !x.IsDeleted, cancellationToken);
+        if (blogPost == null)
+            throw new NotFoundException(nameof(BlogPost), request.BlogPostId);
+
+        var entity = new BlogPostImage
+        {
+            BlogPostId = request.BlogPostId,
+            ImagePath = request.ImagePath,
+            ThumbnailPath = request.ThumbnailPath,
+            AltText = request.AltText,
+            Caption = request.Caption,
+            SortOrder = request.SortOrder
+        };
+
+        _context.BlogPostImages.Add(entity);
+        await _context.SaveChangesAsync(cancellationToken);
+
+        return entity.Id;
+    }
+}

src/CMSMicroservice.Application/BlogPostImageCQ/Commands/AddBlogPostImage/AddBlogPostImageCommandValidator.cs

@@ -0,0 +1,21 @@
+using FluentValidation;
+
+namespace CMSMicroservice.Application.BlogPostImageCQ.Commands.AddBlogPostImage;
+
+public class AddBlogPostImageCommandValidator : AbstractValidator<AddBlogPostImageCommand>
+{
+    public AddBlogPostImageCommandValidator()
+    {
+        RuleFor(x => x.BlogPostId)
+            .GreaterThan(0).WithMessage("شناسه پست نامعتبر است");
+
+        RuleFor(x => x.ImagePath)
+            .NotEmpty().WithMessage("مسیر تصویر الزامی است");
+
+        RuleFor(x => x.AltText)
+            .MaximumLength(500).WithMessage("متن جایگزین حداکثر ۵۰۰ کاراکتر");
+
+        RuleFor(x => x.Caption)
+            .MaximumLength(1000).WithMessage("عنوان تصویر حداکثر ۱۰۰۰ کاراکتر");
+    }
+}