core: implement loan credit scoring pipeline

[EmeditWeb]

Problem

Loan approval is currently manual. There is no
automated credit assessment.

What To Build

1. Create src/modules/credit-scoring/ module
2. Auto-approval / auto-reject / manual review rules
3. POST /loans/:id/assess endpoint

Files To Touch

• src/modules/credit-scoring/ (new)
• src/modules/loans/loans.service.ts
• src/modules/loans/loans.controller.ts
• supabase/migrations/[ts]_loans_under_review.sql

Acceptance Criteria

• Assessment runs automatically on loan creation
• Auto-approve works for qualified borrowers
• Auto-reject works for unqualified applications
• Manual review flagged for edge cases
• npm run build passes

Mandatory Checks Before PR

• npm run build passes
• No any types
• Unit tests for scoring logic
• PR references this issue