feat(content): eager invalidation and optimistic lock for cqrs

M4: ADR-038 Eager Invalidation + ADR-039 Optimistic Lock

- EagerInvalidationService: Redis DEL after MySQL commit

- Cache key conventions for textbook/chapter/kp/question

- Version header check (If-Match/X-Expected-Version) on write endpoints

- 409 Conflict on version mismatch

- All write endpoints return updatedAt timestamp

services/content/src/questions/questions.module.ts

@@ -3,9 +3,10 @@ import { QuestionsController } from "./questions.controller.js";
 import { QuestionsService } from "./questions.service.js";
 import { QuestionsRepository } from "./questions.repository.js";
 import { OutboxModule } from "../shared/outbox/outbox.module.js";
+import { CacheModule } from "../shared/cache/cache.module.js";
 
 @Module({
-  imports: [OutboxModule],
+  imports: [OutboxModule, CacheModule],
   controllers: [QuestionsController],
   providers: [QuestionsService, QuestionsRepository],
   exports: [QuestionsService, QuestionsRepository],