feat: 시즌별 마케팅 + 공지사항 관리 기능 추가

- 연간 세무 캘린더(7개 시즌) 기반 자동 Hero 섹션 전환
- 시즌 감지 시 D-Day 카운트다운, 긴박감 배지, 시즌 CTA 표시
- 서비스 카드 순서 시즌 관련 항목 우선 정렬
- 어드민 공지사항 CRUD (등록·수정·삭제, 기간·유형 설정)
- 홈페이지 상단 공지 배너 자동 노출 (일반/배너/긴급)
- CLAUDE.md에 세무 캘린더 및 마케팅 방향 하네스 추가

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

TaxBaik.Web/Pages/Index.cshtml.cs

@@ -1,4 +1,5 @@
 using Microsoft.AspNetCore.Mvc.RazorPages;
+using TaxBaik.Application.Seasonal;
 using TaxBaik.Application.Services;
 using TaxBaik.Domain.Entities;
 
@@ -7,16 +8,36 @@ namespace TaxBaik.Web.Pages;
 public class IndexModel : PageModel
 {
     private readonly BlogService _blogService;
+    private readonly SeasonalMarketingService _seasonalMarketingService;
+    private readonly AnnouncementService _announcementService;
 
     public List<BlogPost> RecentPosts { get; set; } = [];
+    public CurrentSeasonDto? CurrentSeason { get; set; }
+    public List<Announcement> ActiveAnnouncements { get; set; } = [];
 
-    public IndexModel(BlogService blogService)
+    public IndexModel(
+        BlogService blogService,
+        SeasonalMarketingService seasonalMarketingService,
+        AnnouncementService announcementService)
     {
         _blogService = blogService;
+        _seasonalMarketingService = seasonalMarketingService;
+        _announcementService = announcementService;
     }
 
     public async Task OnGetAsync()
     {
+        CurrentSeason = _seasonalMarketingService.GetCurrentSeason();
+
+        try
+        {
+            ActiveAnnouncements = (await _announcementService.GetActiveAsync()).ToList();
+        }
+        catch
+        {
+            ActiveAnnouncements = [];
+        }
+
         try
         {
             var (posts, _) = await _blogService.GetPublishedPagedAsync(1, 3);