Align admin list empty states and blog category guard

src/TaxBaik.Application/Services/BlogService.cs

@@ -8,7 +8,11 @@ using TaxBaik.Domain.Interfaces;
 
 using Microsoft.Extensions.Caching.Memory;
 
-public class BlogService(IBlogPostRepository repository, IMemoryCache memoryCache, IValidator<CreateBlogPostDto> validator)
+public class BlogService(
+    IBlogPostRepository repository,
+    ICategoryRepository categoryRepository,
+    IMemoryCache memoryCache,
+    IValidator<CreateBlogPostDto> validator)
 {
     public async Task<BlogPost?> GetByIdAsync(int id, CancellationToken ct = default) =>
         await repository.GetByIdAsync(id, ct);
@@ -62,6 +66,7 @@ public class BlogService(IBlogPostRepository repository, IMemoryCache memoryCach
     public async Task<BlogPost> CreateAsync(CreateBlogPostDto dto, CancellationToken ct = default)
     {
         validator.ValidateAndThrow(dto);
+        dto.CategoryId = await EnsureCategoryIdAsync(dto.CategoryId, ct);
         var post = new BlogPost
         {
             Title = dto.Title,
@@ -90,6 +95,7 @@ public class BlogService(IBlogPostRepository repository, IMemoryCache memoryCach
     public async Task<BlogPost?> UpdateAsync(int id, CreateBlogPostDto dto, CancellationToken ct = default)
     {
         validator.ValidateAndThrow(dto);
+        dto.CategoryId = await EnsureCategoryIdAsync(dto.CategoryId, ct);
         var post = await repository.GetByIdAsync(id, ct);
         if (post == null)
             return null;
@@ -178,6 +184,15 @@ public class BlogService(IBlogPostRepository repository, IMemoryCache memoryCach
 
     private static int NormalizePageSize(int pageSize) => Math.Clamp(pageSize, 1, 100);
 
+    private async Task<int> EnsureCategoryIdAsync(int categoryId, CancellationToken ct)
+    {
+        if (categoryId > 0)
+            return categoryId;
+
+        var firstCategory = (await categoryRepository.GetAllAsync(ct)).FirstOrDefault();
+        return firstCategory?.Id ?? throw new ValidationException("블로그 카테고리를 먼저 생성하세요.");
+    }
+
     public async Task<(int TotalPosts, int PublishedPosts)> GetStatsAsync(CancellationToken ct = default)
     {
         var posts = (await repository.GetAllForAdminAsync(ct)).ToList();