fix(scores): rewrite scoreDecayService against actual scores schema

[MarvyNwaokobia]

Summary

• Rewrote scoreDecayService.ts to query the real scores table (user_id, current_score) instead of the non-existent borrowers table
• Rewrote scoreDecayJob.ts with Winston logger (replacing console.*), a Redis distributed lock, and proper error handling
• Wired startScoreDecayCron() into index.ts — runs daily at 02:00 UTC
• Updated existing test in src/cron/__tests__/ and added comprehensive tests in src/tests/
• Documented the score decay decision in src/services/README.md

Design decisions

• Score decay is a real feature — a lending platform needs score degradation for inactive borrowers to reflect current creditworthiness
• 5 points/month decay with floor at 300 (platform minimum), matching existing score bounds (300–850)
• 30-day inactivity threshold based on last LoanRepaid event in contract_events

Test plan

• All 6 score decay tests pass (npm test -- --testPathPattern=scoreDecay)
• TypeScript compiles without errors
• Verify with seeded DB that decay is applied correctly to inactive borrowers
• Verify lock prevents duplicate runs across instances

Closes #7

[ogazboiz]

thanks for tackling this, the decay logic itself is sound (5 pts/month, Math.floor months since last repay, floored at MIN_SCORE 300, wrapped in a redis lock). but there's a real schema mismatch that defeats the purpose of the PR, plus prettier:

1. column names. the PR aims to rewrite scoreDecayService "against the actual scores schema", but it uses s.user_id and s.current_score (scoreDecayService.ts:17, and UPDATE scores SET current_score = $1 ... WHERE user_id = $2 at :45-46). running the actual migrations (1771691269865_initial-schema + 1789000000000_ensure-core-tables) produces a scores table with columns borrower, score, updated_at, no user_id / current_score. so against the migrated DB this throws "column does not exist".

   important nuance: the existing scoresService.ts / scoreReconciliationService.ts on main ALSO use user_id/current_score, so there's a repo-wide inconsistency between the app code and the migrated schema, and your tests pass only because they mock the DB. please confirm the actual column names against the live/migrated schema and align this service to them (likely SELECT s.borrower AS user_id, s.score AS current_score and UPDATE scores SET score = ... WHERE borrower = ...). if the canonical schema really is user_id/current_score, point me at the migration that defines it and i'll recheck.

2. prettier fails on src/services/scoreDecayService.ts:30 and src/cron/tests/scoreDecayJob.test.ts (~9, 43). run: npx prettier --write src/services/scoreDecayService.ts "src/cron/tests/scoreDecayJob.test.ts"

heads up: CI run is gated (first PR), i'll approve it for signal. the schema one is the real blocker, want to make sure this actually runs against the DB.

if you want to keep contributing, join us on Telegram: https://t.me/+DOylgFv1jyJlNzM0

[ogazboiz]

both items from last round are fixed, merging once ci is green. the column mismatch is resolved, it now selects s.borrower AS user_id, s.score AS current_score and does UPDATE scores SET score = ... WHERE borrower = ..., which matches the actual migrated schema (scores(borrower, score, updated_at)), so it runs correctly against the DB now, and prettier passes. decay logic + redis lock unchanged. good.

if you want to keep contributing, join us on Telegram: https://t.me/+DOylgFv1jyJlNzM0

ps: CI is red right now on the migrate step, but that is a pre-existing main-branch issue (a commonjs migration file under our ESM package), nothing to do with your change. once that is sorted this lands.