feat: Implement issues #1228, #1239, #1227, #1238

[trinnode]

Summary

Implements 4 new features for YieldVault-RWA:

#1228: Mock BENJI Strategy Connector

• Added MockBenjiStrategy contract in contracts/mock-strategy/src/mock_benji_strategy.rs
• Implements the same StrategyTrait interface as the production BenjiStrategy
• Configurable NAV for testing yield accrual
• 5 passing tests covering initialization, deposit/withdraw, epoch advancement, NAV updates

#1239: Localized Number Formatting

• Added useLocalizedFormat hook in frontend/src/hooks/useLocalizedFormat.ts
• Provides locale-aware formatting functions (number, currency, percent, compact, date)
• Automatically uses user's preferred locale from PreferencesContext
• 7 passing tests

#1227: Vault Health Metrics Dashboard

• Added VaultHealthDashboard page at /vault-health route
• Displays vault health status with summary cards (healthy count, avg latency, uptime)
• Time range filtering (24h, 7d, 30d, All)
• Backend API endpoint mounted at /api/v1/vault/summary
• Updated vaultHealthApi.ts with typed metrics response

#1238: Audit Log for Vault State Changes

• Added audit_events.rs contract module with timestamped events for deposits, withdrawals, strategy switches, and parameter changes
• Added AuditLog page at /audit-log route with operation and actor filtering
• Backend auditLogEndpoints.ts with paginated endpoint at /api/v1/audit-logs
• Integrated audit event emission into vault deposit, withdraw, and set_strategy functions

Pre-existing Fixes

• Fixed lint/type errors in NetworkSwitchNotification, TransactionStatusModal, ViewState, etc.
• Zero new CI failures introduced

Closes #1228
Closes #1239
Closes #1227
Closes #1238

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