feat(front-hall): implement three-mode layout with quick links panel

Phase 2 of Organizr Migration - Front Hall restructure:

- Add FrontHallState provider with three modes (dashboard, iframe, settings)
- Create QuickLinksPanel widget with categorized links and overflow menus
- Add IframeView with platform-aware implementation (web iframe, mobile fallback)
- Extract DashboardContent from FrontHallPage
- Add QuickLinkSettingsContent placeholder for Phase 4 link editor
- Implement QuickLink entity and data layer with Core API datasource
- Add default quick links fallback when API unavailable
- Update UI_LAYOUT.md with Front Hall panel configurations

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

lib/features/front_hall/data/models/quick_link_model.dart

@@ -0,0 +1,61 @@
+import 'package:freezed_annotation/freezed_annotation.dart';
+import 'package:tatlock_ui/features/front_hall/domain/entities/quick_link.dart';
+
+part 'quick_link_model.freezed.dart';
+part 'quick_link_model.g.dart';
+
+/// Quick link data model for API serialization.
+@freezed
+sealed class QuickLinkModel with _$QuickLinkModel {
+  const factory QuickLinkModel({
+    required String id,
+    required String name,
+    required String url,
+    @JsonKey(name: 'icon_name') required String iconName,
+    String? category,
+    @Default('iframe') String type,
+    @JsonKey(name: 'sort_order') @Default(0) int sortOrder,
+    @JsonKey(name: 'is_active') @Default(true) bool isActive,
+  }) = _QuickLinkModel;
+
+  const QuickLinkModel._();
+
+  factory QuickLinkModel.fromJson(Map<String, dynamic> json) =>
+      _$QuickLinkModelFromJson(json);
+
+  /// Converts to domain entity.
+  QuickLink toEntity() {
+    return QuickLink(
+      id: id,
+      name: name,
+      url: url,
+      iconName: iconName,
+      category: category,
+      type: _parseType(type),
+      sortOrder: sortOrder,
+      isActive: isActive,
+    );
+  }
+
+  /// Creates model from domain entity.
+  factory QuickLinkModel.fromEntity(QuickLink entity) {
+    return QuickLinkModel(
+      id: entity.id,
+      name: entity.name,
+      url: entity.url,
+      iconName: entity.iconName,
+      category: entity.category,
+      type: entity.type == QuickLinkType.iframe ? 'iframe' : 'new_tab',
+      sortOrder: entity.sortOrder,
+      isActive: entity.isActive,
+    );
+  }
+
+  QuickLinkType _parseType(String type) {
+    return switch (type.toLowerCase()) {
+      'iframe' => QuickLinkType.iframe,
+      'new_tab' || 'newtab' => QuickLinkType.newTab,
+      _ => QuickLinkType.iframe,
+    };
+  }
+}