feat: implement cache layer, CSP improvements, and database performance optimizations

- Add Redis cache implementation with LRU eviction
- Enhance Content Security Policy with nonce generation
- Optimize database queries with connection pooling
- Add cache invalidation API endpoints
- Improve security monitoring performance

middleware.ts

@@ -1,5 +1,5 @@
 import { type NextRequest, NextResponse } from "next/server";
-import { buildCSP, generateNonce } from "@/lib/csp";
+import { buildCSP, generateNonce } from "@/lib/csp-server";
 
 export function middleware(request: NextRequest) {
   // Skip CSP for API routes (except CSP report endpoint)