feat: add Student-User association and activate all notification TODOs

apps/server/src/bills/bills.module.ts

@@ -8,6 +8,7 @@ import { PersonalExpense } from '../entities/personal-expense.entity';
 import { Occupancy } from '../entities/occupancy.entity';
 import { Room } from '../entities/room.entity';
 import { Deposit } from '../entities/deposit.entity';
+import { Student } from '../entities/student.entity';
 import { BillsService } from './bills.service';
 import { BillsExportService } from './bills-export.service';
 import { BillsController } from './bills.controller';
@@ -22,6 +23,7 @@ import { BillsController } from './bills.controller';
       Occupancy,
       Room,
       Deposit,
+      Student,
     ]),
     NotificationsModule,
   ],