Security: Add lending pool rate manipulation detection and prevention

[devdianax]

Context

Interest rate models can be manipulated by depositing/withdrawing large amounts to temporarily change rates.

Current Limitation/Problem

Rate manipulation can cause losses for lenders or borrowers who transact during manipulated periods.

Expected Outcome

Rate manipulation detection that flags abnormal rate changes and triggers protective measures.

Acceptance Criteria

• Monitor: utilization rate change per block, rate deviation from TWAP
• Thresholds: alert on >10% rate change in single block, pause on >25%
• Rate TWAP: time-weighted average rate for reference
• Protective measures: delay large rate changes, cap per-block rate change
• Manipulation attempt logging: address, amount, rate impact
• Rate manipulation dashboard: flagged events, historical manipulation attempts
• Governance: adjust thresholds, whitelist known aggregators

Technical Scope

• contracts/lending-pool/src/rate-guard.rs - rate manipulation guard
• backend/src/services/risk/rate-monitor.ts - monitoring service
• Frontend: rate manipulation alerts and dashboard
• Edge cases: legitimate large deposits/withdrawals, flash loan rate impact