refactor: Phase 7-3 Complete - All Blazor pages API-First migration

**Blazor Pages Refactored (9 pages):**
✅ ClientList.razor (Service → IClientBrowserClient)
✅ ClientEdit.razor (Service → IClientBrowserClient)
✅ TaxFilingList.razor (Service → ITaxFilingBrowserClient)
✅ FilingTable.razor (Service → ITaxFilingBrowserClient)
✅ FaqList.razor (Service → IFaqBrowserClient)
✅ FaqEdit.razor (Service → IFaqBrowserClient)
✅ AnnouncementList.razor (Service → IAnnouncementBrowserClient)
✅ AnnouncementEdit.razor (Service → IAnnouncementBrowserClient)
✅ Previously: Dashboard, InquiryTable, InquiryDetail

**Pattern Applied Consistently:**
- Removed all direct service injections (Service Layer)
- Injected specialized Browser Clients (API Layer)
- Error handling with Snackbar notifications
- Try-catch for all API calls
- Graceful fallbacks (empty lists on error)

**Phase 7 Complete: 100% API-First Refactoring**

All admin pages now use:
ClientBrowserClient → /api/client (Clients)
TaxFilingBrowserClient → /api/tax-filing (Tax Filings)
FaqBrowserClient → /api/faq (FAQs)
AnnouncementBrowserClient → /api/announcement (Announcements)
InquiryBrowserClient → /api/inquiry (Inquiries)
AdminDashboardClient → /api/admin-dashboard (Dashboard)

**SOLID + Maintainability Achieved:**
✓ Single Responsibility: Each client = one domain
✓ Open/Closed: Extensible without modifying Blazor
✓ Dependency Inversion: Blazor → Abstractions, not services
✓ Interface Segregation: Fine-grained client interfaces
✓ Liskov Substitution: Interchangeable implementations

Build: ✅ Success (0 errors)
Status: Ready for Phase 6 (SignalR Integration)

Next: NotificationHub for real-time dashboard updates

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

TaxBaik.Web/Components/Admin/Pages/TaxFilings/FilingTable.razor

@@ -1,5 +1,6 @@
-@using TaxBaik.Application.Services
-@inject TaxFilingService FilingService
+@using TaxBaik.Web.Services
+@using TaxBaik.Domain.Entities
+@inject ITaxFilingBrowserClient FilingClient
 @inject ISnackbar Snackbar
 
 @if (Filings == null || Filings.Count == 0)
@@ -58,23 +59,51 @@ else
 
 @code {
     [Parameter]
-    public List<Domain.Entities.TaxFiling>? Filings { get; set; }
+    public List<TaxFiling>? Filings { get; set; }
 
     [Parameter]
     public EventCallback OnStatusChange { get; set; }
 
-    private async Task MarkFiled(Domain.Entities.TaxFiling filing)
+    private async Task MarkFiled(TaxFiling filing)
     {
-        filing.Status = "filed";
-        await FilingService.UpdateAsync(filing);
-        Snackbar.Add("신고 완료 처리되었습니다.", Severity.Success);
-        await OnStatusChange.InvokeAsync();
+        try
+        {
+            filing.Status = "filed";
+            var result = await FilingClient.UpdateAsync(filing.Id, filing);
+            if (result != null)
+            {
+                Snackbar.Add("신고 완료 처리되었습니다.", Severity.Success);
+                await OnStatusChange.InvokeAsync();
+            }
+            else
+            {
+                Snackbar.Add("처리 실패", Severity.Error);
+            }
+        }
+        catch (Exception ex)
+        {
+            Snackbar.Add($"오류: {ex.Message}", Severity.Error);
+        }
     }
 
     private async Task DeleteFiling(int id)
     {
-        await FilingService.DeleteAsync(id);
-        Snackbar.Add("삭제되었습니다.", Severity.Info);
-        await OnStatusChange.InvokeAsync();
+        try
+        {
+            var success = await FilingClient.DeleteAsync(id);
+            if (success)
+            {
+                Snackbar.Add("삭제되었습니다.", Severity.Info);
+                await OnStatusChange.InvokeAsync();
+            }
+            else
+            {
+                Snackbar.Add("삭제 실패", Severity.Error);
+            }
+        }
+        catch (Exception ex)
+        {
+            Snackbar.Add($"오류: {ex.Message}", Severity.Error);
+        }
     }
 }