feat: implement API-first architecture Phase 1 - Dashboard API

**Architecture Refactor (SOLID Principles):**
- Implement AdminDashboardController (REST API)
- Add dashboard summary endpoint
- Add upcoming filings endpoint
- Add recent inquiries endpoint
- Add monthly statistics endpoint

**Database Layer (Repository Pattern):**
- Extend IInquiryRepository with date range queries
- Implement CountByDateRangeAsync
- Implement CountByStatusAndDateAsync
- Extend InquiryRepository with new methods

**Service Layer (Single Responsibility):**
- Extend AdminDashboardService with API methods
- Add GetRecentInquiriesAsync
- Add GetMonthlyStatsAsync with caching

**Test Coverage:**
- Update FakeInquiryRepository mock with new methods

**SOLID Application:**
✓ Single Responsibility: Each class has one reason to change
✓ Open/Closed: Dashboard API can be extended without modifying existing code
✓ Dependency Inversion: Service depends on Repository abstraction
✓ Interface Segregation: API endpoints are focused and specific

Status: ✓ Compiles successfully (0 errors, 0 warnings)

Next phases:
- Add remaining API controllers (Announcement, Client, FAQ, TaxFiling)
- Refactor Blazor components to use API instead of services
- Implement JWT token refresh mechanism
- Add SignalR for change notifications

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

TaxBaik.Application/Services/AdminDashboardService.cs

@@ -40,4 +40,48 @@ public class AdminDashboardService(
         memoryCache.Set(CacheKey, summary, CacheDuration);
         return summary;
     }
+
+    /// <summary>
+    /// 최근 문의 조회
+    /// </summary>
+    public async Task<IReadOnlyList<Inquiry>> GetRecentInquiriesAsync(int limit, CancellationToken ct = default)
+    {
+        var (inquiries, _) = await inquiryService.GetPagedAsync(1, limit, ct: ct);
+        return inquiries.OrderByDescending(x => x.CreatedAt).ToList();
+    }
+
+    /// <summary>
+    /// 월별 통계 (접수 건수, 진행 중, 완료)
+    /// </summary>
+    public async Task<object> GetMonthlyStatsAsync(string? month, CancellationToken ct = default)
+    {
+        var targetMonth = month != null && DateTime.TryParse($"{month}-01", out var dt)
+            ? dt
+            : DateTime.Today;
+
+        var startDate = new DateTime(targetMonth.Year, targetMonth.Month, 1);
+        var endDate = startDate.AddMonths(1).AddDays(-1);
+
+        // 캐시 시도 (일 단위)
+        var cacheKey = $"admin-stats-{startDate:yyyy-MM}";
+        if (memoryCache.TryGetValue(cacheKey, out object? cachedStats) && cachedStats != null)
+            return cachedStats;
+
+        var total = await inquiryService.CountByDateRangeAsync(startDate, endDate, ct);
+        var consulting = await inquiryService.CountByStatusAndDateAsync("consulting", startDate, endDate, ct);
+        var completed = await inquiryService.CountByStatusAndDateAsync("contracted", startDate, endDate, ct);
+
+        var result = new
+        {
+            month = startDate.ToString("yyyy-MM"),
+            totalInquiries = total,
+            consultingCount = consulting,
+            completedCount = completed,
+            newCount = total - consulting - completed,
+            completionRate = total > 0 ? (completed * 100.0 / total) : 0.0
+        };
+
+        memoryCache.Set(cacheKey, result, TimeSpan.FromHours(1));
+        return result;
+    }
 }

TaxBaik.Application/Services/InquiryService.cs

@@ -60,6 +60,12 @@ public class InquiryService(
     public Task<int> CountByStatusAsync(string status, CancellationToken ct = default)
         => repository.CountByStatusAsync(status, ct);
 
+    public Task<int> CountByDateRangeAsync(DateTime startDate, DateTime endDate, CancellationToken ct = default)
+        => repository.CountByDateRangeAsync(startDate, endDate, ct);
+
+    public Task<int> CountByStatusAndDateAsync(string status, DateTime startDate, DateTime endDate, CancellationToken ct = default)
+        => repository.CountByStatusAndDateAsync(status, startDate, endDate, ct);
+
     public async Task UpdateAdminMemoAsync(int id, string? adminMemo, CancellationToken ct = default) =>
         await repository.UpdateAdminMemoAsync(id, adminMemo, ct);