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>

middleware.ts

@@ -88,11 +88,15 @@ export function middleware(request: NextRequest) {
       return addHeaders(request, res);
     }
 
-    // Redirect bare routes to locale-prefixed ones
+    // Add locale prefix: rewrite root path (avoids redirect roundtrip), redirect others
     const preferred = pickLocaleFromHeader(request.headers.get("accept-language"));
-    const redirectTarget =
-      pathname === "/" ? `/${preferred}` : `/${preferred}${pathname}${search || ""}`;
-    responseUrl.pathname = redirectTarget;
+    if (pathname === "/") {
+      responseUrl.pathname = `/${preferred}`;
+      const res = NextResponse.rewrite(responseUrl);
+      res.cookies.set("NEXT_LOCALE", preferred, { path: "/" });
+      return addHeaders(request, res);
+    }
+    responseUrl.pathname = `/${preferred}${pathname}${search || ""}`;
     const res = NextResponse.redirect(responseUrl);
     res.cookies.set("NEXT_LOCALE", preferred, { path: "/" });
     return addHeaders(request, res);