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/entities/index.ts

@@ -32,5 +32,4 @@ export { ExamScore } from './exam-score.entity';
 export { LearningRecord } from './learning-record.entity';
 export { ResultArchive } from './result-archive.entity';
 export { ArchiveAttachment } from './archive-attachment.entity';
-export { StudentReport } from './student-report.entity';
 export { StudentDingMapping } from './student-ding-mapping.entity';