core: implement loan default detection BullMQ job

[EmeditWeb]

Problem

There is no automated process to detect and process
loan defaults. If a learner stops paying, the loan
stays Active indefinitely.

What To Build

1. Create src/jobs/default-detection/ module
2. BullMQ repeat job every 6 hours
3. POST /loans/:id/check-default endpoint
4. Supabase storage for results

Files To Touch

• src/jobs/default-detection/ (new module)
• src/modules/loans/loans.controller.ts
• src/modules/loans/loans.service.ts
• supabase/migrations/[ts]_default_detection.sql

Acceptance Criteria

• Job runs every 6 hours automatically
• All Active loans checked each run
• Default correctly triggered on-chain
• Supabase updated after on-chain default
• npm run build passes

Mandatory Checks Before PR

• npm run build passes
• No any types
• PR references this issue

[Iwayemi-Kehinde]

I would like to work on this issue as I have reviewed the scope, I should have a PR Ready in 50 minutes.