Set Up BullMQ Background Queue to Process Document Analysis and Stellar Anchoring Jobs Asynchronously

[mftee]

Description:
Offload document analysis and blockchain anchoring to an independent background job queue using BullMQ and Redis, so uploads return immediately without blocking.

Tasks:

• Create src/queue/queue.module.ts
• Define a document-processing queue with two job types: analyze and anchor
• Create DocumentProcessor (BullMQ worker) that handles analyze jobs by calling RiskAssessmentService and anchor jobs by calling StellarService
• Update the upload endpoint to enqueue an analyze job after creating the document record
• Update POST /api/documents/:id/verify to enqueue an anchor job instead of calling Stellar synchronously

Acceptance Criteria:

• Uploading a document returns immediately with a 202 Accepted status
• The analyze job runs in the background and updates the document risk score
• The anchor job runs and creates a VerificationRecord on completion
• Failed jobs are retried up to 3 times with exponential backoff