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/Announcements/AnnouncementList.razor

@@ -1,8 +1,8 @@
 @page "/admin/announcements"
 @attribute [Authorize]
-@using TaxBaik.Application.Services
+@using TaxBaik.Web.Services
 @using TaxBaik.Domain.Entities
-@inject AnnouncementService AnnouncementService
+@inject IAnnouncementBrowserClient AnnouncementClient
 @inject NavigationManager Navigation
 @inject IDialogService DialogService
 @inject ISnackbar Snackbar
@@ -99,7 +99,15 @@
 
     private async Task LoadAsync()
     {
-        announcements = (await AnnouncementService.GetAllAsync()).ToList();
+        try
+        {
+            announcements = (await AnnouncementClient.GetAllAsync()).ToList();
+        }
+        catch (Exception ex)
+        {
+            Snackbar.Add($"오류: {ex.Message}", Severity.Error);
+            announcements = [];
+        }
     }
 
     private async Task DeleteAsync(Announcement item)
@@ -111,9 +119,23 @@
 
         if (confirmed != true) return;
 
-        await AnnouncementService.DeleteAsync(item.Id);
-        Snackbar.Add("공지사항이 삭제되었습니다.", Severity.Success);
-        await LoadAsync();
+        try
+        {
+            var success = await AnnouncementClient.DeleteAsync(item.Id);
+            if (success)
+            {
+                Snackbar.Add("공지사항이 삭제되었습니다.", Severity.Success);
+                await LoadAsync();
+            }
+            else
+            {
+                Snackbar.Add("삭제 실패", Severity.Error);
+            }
+        }
+        catch (Exception ex)
+        {
+            Snackbar.Add($"오류: {ex.Message}", Severity.Error);
+        }
     }
 
     private static bool IsCurrentlyActive(Announcement a)