fix: comprehensive security and type improvements from PR #20 review

Security Enhancements:
- Implemented proper rate limiting with automatic cleanup for /register and /forgot-password endpoints
- Added memory usage protection with MAX_ENTRIES limit (10000)
- Fixed rate limiter memory leaks by adding cleanup intervals
- Improved IP extraction with x-real-ip and x-client-ip header support

Code Quality Improvements:
- Refactored ProcessingStatusManager from individual functions to class-based architecture
- Maintained backward compatibility with singleton instance pattern
- Fixed TypeScript strict mode violations across the codebase
- Resolved all build errors and type mismatches

UI Component Fixes:
- Removed unused chart components (Charts.tsx, DonutChart.tsx)
- Fixed calendar component type issues by removing unused custom implementations
- Resolved theme provider type imports
- Fixed confetti component default options handling
- Corrected pointer component coordinate type definitions

Type System Improvements:
- Extended NextAuth types to support dual auth systems (regular and platform users)
- Fixed nullable type handling throughout the codebase
- Resolved Prisma JSON field type compatibility issues
- Corrected SessionMessage and ImportRecord interface definitions
- Fixed ES2015 iteration compatibility issues

Database & Performance:
- Updated database pool configuration for Prisma adapter compatibility
- Fixed pagination response structure in user management endpoints
- Improved error handling with proper error class usage

Testing & Build:
- All TypeScript compilation errors resolved
- ESLint warnings remain but no errors
- Build completes successfully with proper static generation

app/dashboard/sessions/page.tsx

@@ -167,7 +167,7 @@ export default function SessionsPage() {
         <CardHeader>
           <div className="flex items-center gap-3">
             <MessageSquare className="h-6 w-6" />
-            <CardTitle as="h2">Chat Sessions</CardTitle>
+            <CardTitle>Chat Sessions</CardTitle>
           </div>
         </CardHeader>
       </Card>
@@ -203,7 +203,7 @@ export default function SessionsPage() {
             <div className="flex items-center justify-between">
               <div className="flex items-center gap-2">
                 <Filter className="h-5 w-5" aria-hidden="true" />
-                <CardTitle as="h2" id={filtersHeadingId} className="text-lg">
+                <CardTitle id={filtersHeadingId} className="text-lg">
                   Filters & Sorting
                 </CardTitle>
               </div>