refactor: enhance security and performance in configuration and API routes

- Update Content Security Policy (CSP) in next.config.ts to avoid `unsafe-eval` in production, improving security against XSS attacks.
- Refactor API routes to enforce admin authentication and session validation, ensuring secure access to sensitive endpoints.
- Optimize analytics data retrieval by using database aggregation instead of loading all records into memory, improving performance and reducing memory usage.
- Implement session token creation and verification for better session management and security across the application.
- Enhance error handling and input validation in various API routes to ensure robustness and prevent potential issues.

components/AnalyticsProvider.tsx

@@ -189,6 +189,7 @@ export const AnalyticsProvider: React.FC<AnalyticsProviderProps> = ({ children }
 
     // Track scroll depth
     let maxScrollDepth = 0;
+    const firedScrollMilestones = new Set<number>();
     const handleScroll = () => {
       try {
         if (typeof window === 'undefined' || typeof document === 'undefined') return;
@@ -202,18 +203,14 @@ export const AnalyticsProvider: React.FC<AnalyticsProviderProps> = ({ children }
           (window.scrollY / (scrollHeight - innerHeight)) * 100
         );
         
-        if (scrollDepth > maxScrollDepth) {
-          maxScrollDepth = scrollDepth;
-          
-          // Track scroll milestones
-          if (scrollDepth >= 25 && scrollDepth < 50 && maxScrollDepth >= 25) {
-            trackEvent('scroll-depth', { depth: 25, url: window.location.pathname });
-          } else if (scrollDepth >= 50 && scrollDepth < 75 && maxScrollDepth >= 50) {
-            trackEvent('scroll-depth', { depth: 50, url: window.location.pathname });
-          } else if (scrollDepth >= 75 && scrollDepth < 90 && maxScrollDepth >= 75) {
-            trackEvent('scroll-depth', { depth: 75, url: window.location.pathname });
-          } else if (scrollDepth >= 90 && maxScrollDepth >= 90) {
-            trackEvent('scroll-depth', { depth: 90, url: window.location.pathname });
+        if (scrollDepth > maxScrollDepth) maxScrollDepth = scrollDepth;
+
+        // Track each milestone once (avoid spamming events on every scroll tick)
+        const milestones = [25, 50, 75, 90];
+        for (const milestone of milestones) {
+          if (maxScrollDepth >= milestone && !firedScrollMilestones.has(milestone)) {
+            firedScrollMilestones.add(milestone);
+            trackEvent('scroll-depth', { depth: milestone, url: window.location.pathname });
           }
         }
       } catch (error) {