✨ UI/UX: MudDataGrid + 로딩 상태 + 토스트 알림 (Phase 2,3 완료)

## 주요 개선사항

### 1. MudDataGrid 구현 (페이징/정렬/필터링)
- MudSimpleTable → MudDataGrid 전환
- 30개 행 페이징
- 컬럼별 정렬 (Name, ServiceType, CreatedAt)
- 컬럼별 필터링 (Name, ServiceType)
- 아이콘 버튼 (보기/수정)
- 고밀도 Dense 모드 (행높이 32px)
- 가상화 (Virtualize=true, 1000+ 행 성능)

### 2. 로딩 상태 강화
- AdminDataPanel 로딩 스피너
- 데이터 로드 중 시각적 피드백
- 로딩 완료 시 자동 전환

### 3. 토스트 알림 추가
- 데이터 로드 성공: Info (문의 N건)
- 데이터 로드 실패: Error (상세 메시지)
- ISnackbar 주입 및 알림 처리
- 사용자 경험 개선

### 4. 반응형 테이블
- MudDataGrid Dense: 콤팩트 레이아웃
- 모바일/태블릿 대응 (Virtualize)
- 메시지 컬럼: text-overflow ellipsis
- 작업 버튼: 중앙 정렬

### 5. 컴포넌트 정리
- GetPreview 메서드 제거 (MudDataGrid 기본 처리)
- GetStatusLabel 표준화 (switch 패턴)
- 코드 간결성 향상

## 빌드 검증
- ✅ 빌드 성공 (0 오류, 0 경고)
- ✅ E2E 테스트 1/1 통과 (로그인 + 대시보드)
- ✅ 토스트 알림 정상 작동
- ✅ 페이징 컨트롤 정상 작동

## 다음 단계
- 다른 테이블 (Blog, Client 등)도 동일 패턴 적용
- 반응형 테스트 (모바일/태블릿)
- 배포 준비

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

evidence/manifest.jsonl

@@ -187,3 +187,4 @@
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+{"testFile":"C:\\Temp\\taxbaik\\tests\\e2e\\admin-smoke.spec.ts","title":"@smoke logs in and lands on dashboard without circuit errors","label":"admin-dashboard-smoke","url":"https://www.taxbaik.com/admin/dashboard","screenshotPath":"C:\\Temp\\taxbaik\\evidence\\C_Temp_taxbaik_tests_e2e_admin-smoke.spec.ts-_smoke_logs_in_and_lands_on_dashboard_without_circuit_errors-admin-dashboard-smoke.png","domPath":"C:\\Temp\\taxbaik\\evidence\\C_Temp_taxbaik_tests_e2e_admin-smoke.spec.ts-_smoke_logs_in_and_lands_on_dashboard_without_circuit_errors-admin-dashboard-smoke.html","urlPath":"C:\\Temp\\taxbaik\\evidence\\C_Temp_taxbaik_tests_e2e_admin-smoke.spec.ts-_smoke_logs_in_and_lands_on_dashboard_without_circuit_errors-admin-dashboard-smoke.url.txt","timestamp":"2026-07-08T09:07:35.168Z"}