[BE-60] Add unit tests for DocumentsService

[mftee]

Overview

DocumentsService is the most-used service in the app (called by queue, risk assessment, and controllers) but has no unit tests.

Test Cases to Cover

• create() — persists and returns document with correct initial status (PENDING)
• findByOwner() — returns only documents belonging to the specified user
• findByFileHash() — returns document when hash matches, returns null when not found
• updateStatus() — correctly transitions status field
• updateRisk() — sets riskScore and riskFlags correctly
• delete() — removes the document record

File

src/documents/documents.service.spec.ts