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.

next.config.ts

@@ -73,6 +73,13 @@ const nextConfig: NextConfig = {
 
   // Security and cache headers
   async headers() {
+    const csp =
+      process.env.NODE_ENV === "production"
+        ? // Avoid `unsafe-eval` in production (reduces XSS impact and enables stronger CSP)
+          "default-src 'self'; script-src 'self' 'unsafe-inline' https://analytics.dk0.dev; script-src-elem 'self' 'unsafe-inline' https://analytics.dk0.dev; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; font-src 'self' https://fonts.gstatic.com data:; img-src 'self' data: https:; connect-src 'self' https://analytics.dk0.dev https://api.quotable.io; frame-ancestors 'none'; base-uri 'self'; form-action 'self';"
+        : // Dev CSP: allow eval for tooling compatibility
+          "default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval' https://analytics.dk0.dev; script-src-elem 'self' 'unsafe-inline' https://analytics.dk0.dev; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; font-src 'self' https://fonts.gstatic.com data:; img-src 'self' data: https:; connect-src 'self' https://analytics.dk0.dev https://api.quotable.io; frame-ancestors 'none'; base-uri 'self'; form-action 'self';";
+
     return [
       {
         source: "/(.*)",
@@ -107,8 +114,7 @@ const nextConfig: NextConfig = {
           },
           {
             key: "Content-Security-Policy",
-            value:
-              "default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval' https://analytics.dk0.dev; script-src-elem 'self' 'unsafe-inline' https://analytics.dk0.dev; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; font-src 'self' https://fonts.gstatic.com data:; img-src 'self' data: https:; connect-src 'self' https://analytics.dk0.dev https://api.quotable.io; frame-ancestors 'none'; base-uri 'self'; form-action 'self';",
+            value: csp,
           },
         ],
       },