P3-02-03-04: audit log, batch ops, transactions

P3-02: audit-log.entity + service, manual logging in controller
  (startSession, submitAnswer, deleteSession, review, forceEnd)
P3-03: POST batch-delete, POST batch-export endpoints + service methods
P3-04: DataSource.transaction for deleteSession + reviewAssessment,
  graph state cleanup on session delete

server/src/assessment/assessment.module.ts

@@ -23,6 +23,8 @@ import { ContentFilterService } from './services/content-filter.service';
 import { QuestionOutlineService } from './services/question-outline.service';
 import { QuestionBankService } from './services/question-bank.service';
 import { ExportService } from './services/export.service';
+import { AuditLog } from './entities/audit-log.entity';
+import { AuditLogService } from './services/audit-log.service';
 
 @Module({
   imports: [
@@ -34,6 +36,7 @@ import { ExportService } from './services/export.service';
       AssessmentCertificate,
       QuestionBank,
       QuestionBankItem,
+      AuditLog,
     ]),
     forwardRef(() => KnowledgeBaseModule),
     forwardRef(() => KnowledgeGroupModule),
@@ -51,6 +54,7 @@ import { ExportService } from './services/export.service';
     QuestionOutlineService,
     QuestionBankService,
     ExportService,
+    AuditLogService,
   ],
   exports: [AssessmentService, TemplateService, QuestionOutlineService, QuestionBankService, ExportService],
 })