feat(notifications): day sheet notification types

Add daySheetId field to NotificationItem model (Brick-managed), extract
notificationTitle/notificationIcon to top-level testable functions, add
five day-sheet notification cases, and wire tap/banner routing for
day-sheet detail and approvals tab.
Co-Authored-By: claude-flow <ruv@ruv.net>

lib/models/notification_item.model.dart

@@ -19,6 +19,8 @@ class NotificationItem extends OfflineFirstWithSupabaseModel {
   final String? itServiceRequestId;
   final String? announcementId;
   final int? messageId;
+  @Sqlite(name: 'day_sheet_id')
+  final String? daySheetId;
   final String type;
   final DateTime createdAt;
   final DateTime? readAt;
@@ -38,6 +40,7 @@ class NotificationItem extends OfflineFirstWithSupabaseModel {
     required this.itServiceRequestId,
     this.announcementId,
     required this.messageId,
+    this.daySheetId,
     required this.type,
     required this.createdAt,
     required this.readAt,
@@ -55,6 +58,7 @@ class NotificationItem extends OfflineFirstWithSupabaseModel {
       itServiceRequestId: map['it_service_request_id'] as String?,
       announcementId: map['announcement_id'] as String?,
       messageId: map['message_id'] as int?,
+      daySheetId: map['day_sheet_id'] as String?,
       type: map['type'] as String? ?? 'mention',
       createdAt: AppTime.parse(map['created_at'] as String),
       readAt: map['read_at'] == null