feat: implement admin inquiry create/edit/delete functionality

Core Components:
- Create reusable InquiryForm.razor component following SOLID principles
- Implement InquiryCreate.razor for registering new inquiries (offline, phone)
- Implement InquiryEdit.razor for modifying existing inquiries with delete
- Add DeleteAsync method to InquiryRepository and InquiryService
- Update InquiryList with 'Create' button and Edit link in table

Architecture:
- InquiryForm: Encapsulates form logic, can be reused for create/edit
- Service Layer: All operations go through InquiryService for cache invalidation
- Repository Pattern: Database operations isolated in InquiryRepository
- UI Consistency: Both pages follow admin-page-hero pattern

Features:
- Admin can create inquiries from phone/offline consultations
- Admin can modify inquiry details (name, phone, email, message, status, memo)
- Admin can delete inquiries with confirmation dialog
- All operations update dashboard cache
- Status validation and error handling throughout

Testing:
- Updated FakeInquiryRepository in tests to implement DeleteAsync

TaxBaik.Web/Components/Admin/Pages/Inquiries/InquiryList.razor

@@ -11,6 +11,8 @@
         <MudText Typo="Typo.h4" Class="admin-page-title">문의 관리</MudText>
         <MudText Typo="Typo.body2" Class="admin-page-subtitle">상담 요청을 상태별로 확인하고 후속 조치를 기록합니다.</MudText>
     </div>
+    <MudButton Variant="Variant.Filled" Color="Color.Primary" StartIcon="@Icons.Material.Filled.Add"
+        Href="/taxbaik/admin/inquiries/create">새 문의 등록</MudButton>
 </section>
 
 <MudPaper Class="admin-surface" Elevation="0">