Add date range filtering and CSV export to audit log UI

[sagnik11]

TL;DR

Add date range filtering (from/to dates) and CSV export functionality to the audit log dashboard, along with environment variables for controlling export limits and data retention policies.

What changed?

• Environment configuration: Added AUDIT_LOG_RETENTION_DAYS and AUDIT_LOG_EXPORT_MAX_ROWS environment variables to .env.example with documentation
• UI filters: Added "From" and "To" date input fields to allow filtering audit logs by date range
• Export functionality: Added "Export CSV" button that downloads filtered audit logs as CSV
• API enhancements:
  • Extracted filter parsing into reusable parseFilters() function
  • Implemented CSV export endpoint with row cap validation (prevents exports exceeding AUDIT_LOG_EXPORT_MAX_ROWS)
  • Added CSV formatting with proper escaping for special characters
  • Returns error if export would exceed configured limit, prompting user to narrow date range
• State management: Added fromDate and toDate state variables, integrated into filter dependencies and reset logic
• UI layout: Restructured header to include both title/description and export button side-by-side