refactor: remove obsolete scaffolding and dead modules

Drop the unused root hello-world controller, empty CommonModule imports, development seeding code, legacy student report entity, stale DTOs, notification hook, and their placeholder tests.

apps/server/src/archive/archive.module.ts

@@ -8,7 +8,6 @@ import { LearningRecord } from '../entities/learning-record.entity';
 import { ResultArchive } from '../entities/result-archive.entity';
 import { ArchiveAttachment } from '../entities/archive-attachment.entity';
 import { AttendanceRecord } from '../entities/attendance-record.entity';
-import { CommonModule } from '../common/common.module';
 import { NotificationsModule } from '../notifications/notifications.module';
 import { ArchiveService } from './archive.service';
 import { ArchiveReportService } from './archive-report.service';
@@ -26,7 +25,6 @@ import { ArchiveController } from './archive.controller';
       ArchiveAttachment,
       AttendanceRecord,
     ]),
-    CommonModule,
     NotificationsModule,
   ],
   controllers: [ArchiveController],