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>

app/components/ClientProviders.tsx

@@ -15,7 +15,7 @@ const BackgroundBlobs = dynamic(() => import("@/components/BackgroundBlobs").cat
 });
 
 const ShaderGradientBackground = dynamic(
-  () => import("./ShaderGradientBackground"),
+  () => import("./ShaderGradientBackground").catch(() => ({ default: () => null })),
   { ssr: false, loading: () => null }
 );