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/Common/Interfaces/IApplicationDbContext.cs

@@ -1,3 +1,5 @@
+using CMSMicroservice.Domain.Entities.Blog;
+using CMSMicroservice.Domain.Entities.Content;
 using CMSMicroservice.Domain.Entities.Payment;
 using CMSMicroservice.Domain.Entities.Order;
 using CMSMicroservice.Domain.Entities.DiscountShop;
@@ -66,6 +68,17 @@ public interface IApplicationDbContext
     DbSet<InventoryItem> InventoryItems { get; }
     DbSet<StockMovement> StockMovements { get; }
     
+    // ============= Blog =============
+    DbSet<BlogPost> BlogPosts { get; }
+    DbSet<BlogCategory> BlogCategories { get; }
+    DbSet<BlogPostCategory> BlogPostCategories { get; }
+    DbSet<BlogPostTag> BlogPostTags { get; }
+    DbSet<BlogPostImage> BlogPostImages { get; }
+    
+    // ============= Content Management =============
+    DbSet<SitePage> SitePages { get; }
+    DbSet<SitePageSection> SitePageSections { get; }
+    
     /// <summary>
     /// دسترسی به DatabaseFacade برای اجرای raw SQL و Stored Procedures
     /// </summary>