Add error handling for audit logs and cache operations

[davigiroux]

Summary

This PR adds proper error handling for audit log insertions and cache operations throughout the flag handler, replacing silent failures with logged errors.

Key Changes

• Added log import to both flags.go and evaluate.go
• Wrapped InsertAuditLog() calls in error checks across all flag operations (Create, Update, Delete, Toggle) with contextual logging
• Wrapped InvalidateFlag() calls in error checks in Update, Delete, and Toggle operations with logging
• Wrapped GetFlag() and SetFlag() cache operations in the Evaluate handler with error checks and logging
• All errors are logged with log.Printf() including the operation type and affected flag key for debugging

Implementation Details

• Errors from audit log operations no longer silently fail; they are logged but don't block the HTTP response
• Cache errors are similarly logged without blocking the response, allowing graceful degradation
• Log messages include context about which operation failed (create, update, delete, toggle, cache get/set) and the flag key involved
• This maintains backward compatibility while improving observability of failures in non-critical operations

https://claude.ai/code/session_01JDqcjWMkkrAyY2CxALpmm3