perf: fix PageSpeed Insights issues (WebGL errors, bfcache, redirects, a11y)

- Add WebGL support detection in ShaderGradientBackground to prevent console errors
- Add .catch() fallback to ShaderGradientBackground dynamic import
- Remove hardcoded aria-label from consent banner minimize button (fixes label-content-name-mismatch)
- Use rewrite instead of redirect for root locale routing (eliminates one redirect hop)
- Change n8n API cache headers from no-store to no-cache (enables bfcache)
- Add three and @react-three/fiber to optimizePackageImports for better tree-shaking

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

next.config.ts

@@ -34,7 +34,7 @@ const nextConfig: NextConfig = {
   experimental:
     process.env.NODE_ENV === "production"
       ? {
-          optimizePackageImports: ["lucide-react", "framer-motion"],
+          optimizePackageImports: ["lucide-react", "framer-motion", "three", "@react-three/fiber"],
         }
       : {
           // In development, enable webpack build worker for faster builds
@@ -167,12 +167,12 @@ const nextConfig: NextConfig = {
         ],
       },
       {
-        // Only prevent caching for real-time/sensitive API routes
+        // Allow bfcache for n8n routes: use no-cache (revalidate) instead of no-store
         source: "/api/n8n/(.*)",
         headers: [
           {
             key: "Cache-Control",
-            value: "no-store, no-cache, must-revalidate, proxy-revalidate",
+            value: "no-cache, must-revalidate",
           },
         ],
       },