feat: implement evidence moderator flags and isHidden logic

[yunus-dev-codecrafter]

closes #217

PR Title: Implement Evidence Moderator Flags and isHidden Logic

📚 Overview

This PR addresses security and integrity concerns identified during the audit (Ref #BE-217) by implementing a robust moderation system for evidence submission. It introduces the ability for moderators to flag evidence, which triggers an automatic "hidden" state to prevent malicious or invalid content from being publicly visible.

🎯 Objectives

• Implement isHidden flag logic for Evidence entities.
• Enable automatic hiding of evidence when flagged by authorized moderators.
• Restrict public access to flagged evidence while maintaining admin visibility.
• Add comprehensive unit tests to ensure logic integrity.

🧩 Key Changes

1. Schema & Entities

• Added isHidden: boolean to evidence.entity.ts.
• Added isModerator: boolean to evidence-flag.entity.ts to distinguish authoritative flags.

2. Business Logic

• evidence-flag.service.ts: Updated createFlag to toggle isHidden on the associated Evidence if the flagger is a moderator.
• evidence.service.ts: Refactored retrieval methods (getEvidence, getEvidenceForClaim) to filter out hidden records by default.

3. API Layer

• claims.controller.ts: Added admin=true query parameter support to bypass visibility filters for administrative views.

✅ Verification Results

• Unit Tests: 11 tests passed across EvidenceService and EvidenceFlagService.
• Protocol Invariants: Confirmed that hidden evidence is unreachable via standard public endpoints but accessible for review via admin-privileged requests.

🛠 Testing Command

npx jest src/claims/evidence-flag.service.spec.ts src/claims/evidence.service.spec.ts

[dDevAhmed]

resolve conflicts @yunus-dev-codecrafter

[yunus-dev-codecrafter]

Conflicts resolved