Feature/multi broker sync - #9

Code Review: 🔴 Requesting Changes

I have reviewed this PR and found a critical security issue that must be fixed before merging, along with a few other observations.

🔴 BLOCKER:

• Authentication Bypass Risk: In DocumentProcessorController.java (resolveUserId), the PR removes the 401 Unauthorized exception and replaces it with a hardcoded fallback to "local-dev-user".
  If this ships to production, any unauthenticated request will successfully process documents and attach them to a shared local-dev-user account, bypassing security. You must restore the 401 Unauthorized throw. (If you need a local bypass for testing, wrap it in a @Profile("!prod & !preprod") check).

🟠 MAJOR:

• Kafka Contract Risk: In MessagingEventService.sendBatchCompletedEvent, you are reusing PortfolioUpdateEvent but passing the batchId as the id field. Does downstream am-portfolio or am-analysis expect that id to strictly be a portfolioId? If downstream queries the database for a Portfolio using that UUID, it will fail. Please verify the Kafka contract.

🟡 MINOR / NIT:

• Memory Pressure (OOM Risk): In DocumentProcessorService.submitBatchSync, you are eagerly calling entry.getFile().getBytes() to load files into memory. For typical 1-2MB PDFs, this is fine, but if a user uploads five 50MB files, that's 250MB loaded directly into heap per request. Ensure spring.servlet.multipart.max-file-size is strictly enforced.
• Test Coverage: Consider adding unit tests for MultiPortfolioSplitterFactory and BrokerDetectionService to ensure the fallback logic works properly.