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.Infrastructure/Repositories/AnnouncementRepository.cs

@@ -0,0 +1,74 @@
+namespace TaxBaik.Infrastructure.Repositories;
+
+using Dapper;
+using TaxBaik.Domain.Entities;
+using TaxBaik.Domain.Interfaces;
+
+public class AnnouncementRepository(IDbConnectionFactory connectionFactory)
+    : BaseRepository(connectionFactory), IAnnouncementRepository
+{
+    private const string SelectColumns =
+        "id, title, content, display_type, is_active, starts_at, ends_at, sort_order, created_at, updated_at";
+
+    public async Task<IEnumerable<Announcement>> GetActiveAsync(CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        return await conn.QueryAsync<Announcement>(
+            $@"SELECT {SelectColumns}
+               FROM announcements
+               WHERE is_active = TRUE
+                 AND (starts_at IS NULL OR starts_at <= NOW())
+                 AND (ends_at   IS NULL OR ends_at   >= NOW())
+               ORDER BY sort_order DESC, created_at DESC");
+    }
+
+    public async Task<IEnumerable<Announcement>> GetAllAsync(CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        return await conn.QueryAsync<Announcement>(
+            $"SELECT {SelectColumns} FROM announcements ORDER BY sort_order DESC, created_at DESC");
+    }
+
+    public async Task<Announcement?> GetByIdAsync(int id, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        return await conn.QueryFirstOrDefaultAsync<Announcement>(
+            $"SELECT {SelectColumns} FROM announcements WHERE id = @Id",
+            new { Id = id });
+    }
+
+    public async Task<int> CreateAsync(Announcement announcement, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        return await conn.QueryFirstAsync<int>(
+            @"INSERT INTO announcements
+                (title, content, display_type, is_active, starts_at, ends_at, sort_order, created_at, updated_at)
+              VALUES
+                (@Title, @Content, @DisplayType, @IsActive, @StartsAt, @EndsAt, @SortOrder, NOW(), NOW())
+              RETURNING id",
+            announcement);
+    }
+
+    public async Task UpdateAsync(Announcement announcement, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        await conn.ExecuteAsync(
+            @"UPDATE announcements
+              SET title        = @Title,
+                  content      = @Content,
+                  display_type = @DisplayType,
+                  is_active    = @IsActive,
+                  starts_at    = @StartsAt,
+                  ends_at      = @EndsAt,
+                  sort_order   = @SortOrder,
+                  updated_at   = NOW()
+              WHERE id = @Id",
+            announcement);
+    }
+
+    public async Task DeleteAsync(int id, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        await conn.ExecuteAsync("DELETE FROM announcements WHERE id = @Id", new { Id = id });
+    }
+}