refactor: Phase 4 - Dashboard Blazor → API client (Service Locator → Dependency Injection)

**Implementation:**
- AdminDashboardClient: HTTP API client interface
  - GetSummaryAsync: Fetch dashboard metrics
  - GetUpcomingFilingsAsync: 30-day filings forecast
  - GetRecentInquiriesAsync: Latest inquiries
  - GetMonthlyStatsAsync: Monthly statistics
- Program.cs: Register IAdminDashboardClient
- Dashboard.razor: Replace service injection with API client
  - Remove: Direct AdminDashboardService/TaxFilingService injection
  - Add: IAdminDashboardClient injection
  - Add: Error handling & loading state
  - Change: OnInitializedAsync() calls API endpoints

**SOLID Principles Applied:**
✓ D (Dependency Inversion): Blazor depends on IAdminDashboardClient abstraction
✓ S (Single Responsibility): Client handles only HTTP communication
✓ O (Open/Closed): Can extend API without changing Blazor component

**Architecture Pattern:**
- Before: Blazor → Service (server-side logic) → Repository → DB
- After: Blazor → HTTP → API → Service → Repository → DB

**Benefits:**
- Clear separation of concerns
- Easier to test (mock HTTP)
- Foundation for token refresh middleware
- Prepare for SignalR integration

Status: Ready for Phase 5 (JWT token refresh)
Next: Implement automatic token refresh on 401 responses

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

TaxBaik.Web/Components/Admin/Pages/Dashboard.razor

@@ -1,8 +1,7 @@
 @page "/admin/dashboard"
 @attribute [Authorize]
-@using TaxBaik.Application.Services
-@inject AdminDashboardService DashboardService
-@inject TaxFilingService FilingService
+@using TaxBaik.Web.Services
+@inject IAdminDashboardClient DashboardClient
 @inject NavigationManager Nav
 
 <PageTitle>대시보드</PageTitle>
@@ -161,14 +160,30 @@
 @code {
     private AdminDashboardSummary summary = new(0, 0, 0, 0, []);
     private List<Domain.Entities.TaxFiling> upcomingFilings = [];
+    private string? errorMessage;
+    private bool isLoading = true;
 
     protected override async Task OnInitializedAsync()
     {
-        var summaryTask = DashboardService.GetSummaryAsync();
-        var filingsTask = FilingService.GetUpcomingAsync(30);
-        await Task.WhenAll(summaryTask, filingsTask);
-        summary = await summaryTask;
-        upcomingFilings = (await filingsTask).ToList();
+        try
+        {
+            // API 클라이언트 사용 (서비스 직접 호출 X)
+            var summaryTask = DashboardClient.GetSummaryAsync();
+            var filingsTask = DashboardClient.GetUpcomingFilingsAsync(30);
+
+            await Task.WhenAll(summaryTask, filingsTask);
+            summary = await summaryTask;
+            upcomingFilings = (await filingsTask).ToList();
+        }
+        catch (Exception ex)
+        {
+            errorMessage = "대시보드 데이터를 불러올 수 없습니다.";
+            Console.Error.WriteLine($"Dashboard error: {ex.Message}");
+        }
+        finally
+        {
+            isLoading = false;
+        }
     }
 
     private static string GetStatusLabel(string status) => InquiryStatusMapper.Labels.GetValueOrDefault(status, status);

TaxBaik.Web/Program.cs

@@ -68,6 +68,7 @@ builder.Services.AddAuthorizationCore();
 
 // HTTP Client for API
 builder.Services.AddHttpClient<IApiClient, ApiClient>();
+builder.Services.AddHttpClient<IAdminDashboardClient, AdminDashboardClient>();
 
 // UI & 캐시
 builder.Services.AddMudServices();

TaxBaik.Web/Services/AdminDashboardClient.cs

@@ -0,0 +1,105 @@
+using System.Net.Http.Json;
+using TaxBaik.Application.Services;
+using TaxBaik.Domain.Entities;
+
+namespace TaxBaik.Web.Services;
+
+/// <summary>
+/// Admin Dashboard API Client
+/// SOLID: Single Responsibility - Dashboard API 호출만 담당
+/// Dependency Inversion - 추상화된 인터페이스 사용
+/// </summary>
+public interface IAdminDashboardClient
+{
+    Task<AdminDashboardSummary> GetSummaryAsync(CancellationToken ct = default);
+    Task<IEnumerable<TaxFiling>> GetUpcomingFilingsAsync(int days = 30, CancellationToken ct = default);
+    Task<IEnumerable<Inquiry>> GetRecentInquiriesAsync(int limit = 10, CancellationToken ct = default);
+    Task<object> GetMonthlyStatsAsync(string? month = null, CancellationToken ct = default);
+}
+
+public class AdminDashboardClient : IAdminDashboardClient
+{
+    private readonly HttpClient _http;
+    private readonly ILogger<AdminDashboardClient> _logger;
+
+    public AdminDashboardClient(HttpClient http, ILogger<AdminDashboardClient> logger)
+    {
+        _http = http;
+        _logger = logger;
+        _http.BaseAddress = new Uri("/taxbaik/api/");
+    }
+
+    public async Task<AdminDashboardSummary> GetSummaryAsync(CancellationToken ct = default)
+    {
+        try
+        {
+            var result = await _http.GetFromJsonAsync<AdminDashboardSummary>(
+                "admin-dashboard/summary", cancellationToken: ct);
+            return result ?? new(0, 0, 0, 0, []);
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "Failed to fetch dashboard summary");
+            throw;
+        }
+    }
+
+    public async Task<IEnumerable<TaxFiling>> GetUpcomingFilingsAsync(int days = 30, CancellationToken ct = default)
+    {
+        try
+        {
+            var result = await _http.GetFromJsonAsync<ApiResponse<TaxFiling>>(
+                $"admin-dashboard/upcoming-filings?days={days}", cancellationToken: ct);
+            return result?.Data ?? [];
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "Failed to fetch upcoming filings");
+            throw;
+        }
+    }
+
+    public async Task<IEnumerable<Inquiry>> GetRecentInquiriesAsync(int limit = 10, CancellationToken ct = default)
+    {
+        try
+        {
+            var result = await _http.GetFromJsonAsync<ApiResponse<Inquiry>>(
+                $"admin-dashboard/recent-inquiries?limit={limit}", cancellationToken: ct);
+            return result?.Data ?? [];
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "Failed to fetch recent inquiries");
+            throw;
+        }
+    }
+
+    public async Task<object> GetMonthlyStatsAsync(string? month = null, CancellationToken ct = default)
+    {
+        try
+        {
+            var url = "admin-dashboard/monthly-stats";
+            if (!string.IsNullOrEmpty(month))
+                url += $"?month={month}";
+
+            var result = await _http.GetFromJsonAsync<object>(url, cancellationToken: ct);
+            return result ?? new();
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "Failed to fetch monthly stats");
+            throw;
+        }
+    }
+}
+
+/// <summary>
+/// API Response wrapper
+/// </summary>
+internal class ApiResponse<T>
+{
+    public IEnumerable<T>? Data { get; set; }
+    public int Total { get; set; }
+    public int Page { get; set; }
+    public int PageSize { get; set; }
+}