feat: SMS 스캔 패키지를 flutter_sms_inbox로 변경 및 플랫폼별 최적화

- telephony 패키지를 flutter_sms_inbox로 교체
- 플랫폼별 SMS 스캔 로직 구현:
  * Web: mock data 사용
  * Android: flutter_sms_inbox로 실제 SMS 스캔
  * iOS: SMS 기능 비활성화
- iOS에서 SMS 스캔 버튼 숨김 처리
- PlatformHelper 유틸리티 추가로 웹 환경 오류 해결
- Android 네이티브 MethodChannel 코드 제거

lib/widgets/floating_navigation_bar.dart

@@ -3,6 +3,7 @@ import 'package:flutter/services.dart';
 import '../theme/app_colors.dart';
 import 'glassmorphism_card.dart';
 import '../l10n/app_localizations.dart';
+import '../utils/platform_helper.dart';
 
 class FloatingNavigationBar extends StatefulWidget {
   final int selectedIndex;
@@ -117,17 +118,18 @@ class _FloatingNavigationBarState extends State<FloatingNavigationBar>
                         _AddButton(
                           onTap: () => _onItemTapped(2),
                         ),
-                        _NavigationItem(
-                          icon: Icons.qr_code_scanner_rounded,
-                          label: AppLocalizations.of(context).smsScanLabel,
-                          isSelected: widget.selectedIndex == 3,
-                          onTap: () => _onItemTapped(3),
-                        ),
+                        if (!PlatformHelper.isIOS)
+                          _NavigationItem(
+                            icon: Icons.qr_code_scanner_rounded,
+                            label: AppLocalizations.of(context).smsScanLabel,
+                            isSelected: widget.selectedIndex == 3,
+                            onTap: () => _onItemTapped(3),
+                          ),
                         _NavigationItem(
                           icon: Icons.settings_rounded,
                           label: AppLocalizations.of(context).settings,
-                          isSelected: widget.selectedIndex == 4,
-                          onTap: () => _onItemTapped(4),
+                          isSelected: PlatformHelper.isIOS ? widget.selectedIndex == 3 : widget.selectedIndex == 4,
+                          onTap: () => _onItemTapped(PlatformHelper.isIOS ? 3 : 4),
                         ),
                       ],
                     ),