feat: 블로그 시즌 연동 — 홈페이지 세무 정보 섹션 시즌화

- TaxSeason / CurrentSeasonDto에 RelatedCategorySlug 추가
- TaxSeasonCalendar 각 시즌에 카테고리 슬러그 매핑
  (income-tax→income-tax, vat-1st/2nd→vat, 종부세→real-estate-tax 등)
- IBlogPostRepository.GetByCategorySlugAsync 추가
- BlogService.GetSeasonalPostsAsync: 시즌 관련 글 2개 우선 + 나머지 최신 글로 채움
- IndexModel: SeasonalPosts / RecentPosts 분리 로드
- Index.cshtml 블로그 섹션: 시즌 중 "이번 시즌 추천" 배지 + 시즌별 전체보기 버튼
- site.css: blog-card--seasonal, seasonal-blog-tag, btn-seasonal 스타일

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

TaxBaik.Infrastructure/Repositories/BlogPostRepository.cs

@@ -58,6 +58,21 @@ public class BlogPostRepository(IDbConnectionFactory connectionFactory) : BaseRe
         return (items, total);
     }
 
+    public async Task<IEnumerable<BlogPost>> GetByCategorySlugAsync(string categorySlug, int limit, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        return await conn.QueryAsync<BlogPost>(
+            @"SELECT bp.id, bp.title, bp.slug, bp.category_id, bp.tags,
+                     bp.published_at, bp.view_count, bp.seo_description, bp.thumbnail_url,
+                     bp.is_published, bp.created_at, bp.updated_at, c.name AS category_name
+              FROM blog_posts bp
+              LEFT JOIN categories c ON bp.category_id = c.id
+              WHERE bp.is_published = TRUE AND c.slug = @CategorySlug
+              ORDER BY bp.published_at DESC
+              LIMIT @Limit",
+            new { CategorySlug = categorySlug, Limit = limit });
+    }
+
     public async Task<IEnumerable<BlogPost>> GetAllForAdminAsync(CancellationToken cancellationToken = default)
     {
         using var conn = Conn();