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/Queries/GetBlogPostImages/GetBlogPostImagesQuery.cs

@@ -0,0 +1,19 @@
+using MediatR;
+
+namespace CMSMicroservice.Application.BlogPostImageCQ.Queries.GetBlogPostImages;
+
+public class GetBlogPostImagesQuery : IRequest<List<BlogPostImageDto>>
+{
+    public long BlogPostId { get; set; }
+}
+
+public class BlogPostImageDto
+{
+    public long Id { get; set; }
+    public long BlogPostId { get; set; }
+    public string ImagePath { get; set; } = default!;
+    public string? ThumbnailPath { get; set; }
+    public string? AltText { get; set; }
+    public string? Caption { get; set; }
+    public int SortOrder { get; set; }
+}

src/CMSMicroservice.Application/BlogPostImageCQ/Queries/GetBlogPostImages/GetBlogPostImagesQueryHandler.cs

@@ -0,0 +1,35 @@
+using CMSMicroservice.Application.Common.Interfaces;
+using MediatR;
+using Microsoft.EntityFrameworkCore;
+
+namespace CMSMicroservice.Application.BlogPostImageCQ.Queries.GetBlogPostImages;
+
+public class GetBlogPostImagesQueryHandler : IRequestHandler<GetBlogPostImagesQuery, List<BlogPostImageDto>>
+{
+    private readonly IApplicationDbContext _context;
+
+    public GetBlogPostImagesQueryHandler(IApplicationDbContext context)
+    {
+        _context = context;
+    }
+
+    public async Task<List<BlogPostImageDto>> Handle(GetBlogPostImagesQuery request, CancellationToken cancellationToken)
+    {
+        var images = await _context.BlogPostImages
+            .Where(x => x.BlogPostId == request.BlogPostId && !x.IsDeleted)
+            .OrderBy(x => x.SortOrder)
+            .Select(x => new BlogPostImageDto
+            {
+                Id = x.Id,
+                BlogPostId = x.BlogPostId,
+                ImagePath = x.ImagePath,
+                ThumbnailPath = x.ThumbnailPath,
+                AltText = x.AltText,
+                Caption = x.Caption,
+                SortOrder = x.SortOrder
+            })
+            .ToListAsync(cancellationToken);
+
+        return images;
+    }
+}