fix: implement comprehensive UI/UX and code organization improvements

CSRF Form Enhancements:
- Add optional onError callback prop for better error handling
- Remove CSRF token from console logging for security
- Provide user-friendly error notifications instead of silent failures

Date Filter Optimization:
- Refactor sessions route to avoid object mutation issues
- Build date filters cleanly without relying on spreading existing objects
- Prevent potential undefined startTime mutations

Geographic Threat Map Optimization:
- Extract country names to reusable constants in lib/constants/countries.ts
- Calculate max values once to avoid repeated expensive operations
- Centralize threat level color mapping to eliminate duplicated logic
- Replace repeated color assignments with centralized THREAT_LEVELS configuration

Accessibility Improvements:
- Add keyboard support to audit log table rows (Enter/Space keys)
- Include proper ARIA labels and focus management
- Add tabIndex for screen reader compatibility
- Enhance focus indicators with ring styling

Performance & Code Organization:
- Move COUNTRY_NAMES to shared constants for reusability
- Optimize calculation patterns in threat mapping components
- Reduce redundant logic and improve maintainability

app/api/dashboard/sessions/route.ts

@@ -41,19 +41,20 @@ function buildWhereClause(
   }
 
   // Date Range Filter
+  const dateFilters: { gte?: Date; lt?: Date } = {};
+
   if (startDate) {
-    whereClause.startTime = {
-      ...((whereClause.startTime as object) || {}),
-      gte: new Date(startDate),
-    };
+    dateFilters.gte = new Date(startDate);
   }
+
   if (endDate) {
     const inclusiveEndDate = new Date(endDate);
     inclusiveEndDate.setDate(inclusiveEndDate.getDate() + 1);
-    whereClause.startTime = {
-      ...((whereClause.startTime as object) || {}),
-      lt: inclusiveEndDate,
-    };
+    dateFilters.lt = inclusiveEndDate;
+  }
+
+  if (Object.keys(dateFilters).length > 0) {
+    whereClause.startTime = dateFilters;
   }
 
   return whereClause;