fix: route vouching reputation reads through ReputationService

[EmeditWeb]

Problem

In vouching.service.ts (lines 204-219), getLearnerReputationScore() reads directly from the reputation_cache table instead of calling ReputationService.getReputationScore(). This misses the multi-layer cache (Redis → Supabase → contract) and contract-fetch logic.

What To Build

1. Inject ReputationService into VouchingService
2. Replace direct DB query with ReputationService call
3. Verify reputation data is consistent

Files To Touch

• src/modules/vouching/vouching.service.ts — lines 204-219

Acceptance Criteria

• Vouching service uses ReputationService for score lookups
• Consistent cached reputation across the API
• Build passes

Mandatory Checks

• context/ files read
• npm run build passes
• PR references this issue