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/ConsentBanner.tsx

@@ -54,8 +54,6 @@ export default function ConsentBanner() {
             type="button"
             onClick={() => setMinimized(true)}
             className="shrink-0 text-xs text-stone-500 hover:text-stone-900 transition-colors"
-            aria-label="Minimize privacy banner"
-            title="Minimize"
           >
             {s.hide}
           </button>