Prevent task starting and completion without assigned it staff

lib/screens/tasks/task_detail_screen.dart

@@ -3503,12 +3503,8 @@ class _TaskDetailScreenState extends ConsumerState<TaskDetailScreen>
       return chip;
     }
 
-    final statusOptions = _statusOptions.where((status) {
-      if (status == 'in_progress' && !hasAssignedItStaff) {
-        return false;
-      }
-      return true;
-    }).toList();
+    // Show all status options - validation happens on selection
+    final statusOptions = _statusOptions;
 
     return PopupMenuButton<String>(
       onSelected: (value) async {
@@ -3606,6 +3602,16 @@ class _TaskDetailScreenState extends ConsumerState<TaskDetailScreen>
           return;
         }
 
+        // Validate IT staff assignment before starting or completing
+        if ((value == 'in_progress' || value == 'completed') &&
+            !hasAssignedItStaff) {
+          showWarningSnackBar(
+            context,
+            'Please assign at least one IT Staff member before ${value == 'in_progress' ? 'starting' : 'completing'} this task.',
+          );
+          return;
+        }
+
         // Update DB only — Supabase realtime stream will emit the
         // updated task list, so explicit invalidation here causes a
         // visible loading/refresh and is unnecessary.