updated terminology from "Coach" to "Counselor" across multiple files for consistency and clarity

handlers/assignments.php

@@ -70,7 +70,7 @@ case 'POST':
         }
         if (!$chk->fetch()) {
             qdb_discard($tmpDb, $lockFp);
-            json_error('NOT_FOUND', 'Coach not found or not authorized', 404);
+            json_error('NOT_FOUND', 'Counselor not found or not authorized', 404);
         }
 
         [$rbacClause, $rbacParams] = rbac_client_filter($tokenRec);