Fix startup freeze on weak devices and add Vercel Analytics

Defer WebGL shader compile behind a visible boot placeholder, lower initial DPR, disable glass blur during boot, and lighten the intro so the page stays responsive instead of looking half-loaded.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs.html

@@ -170,5 +170,9 @@
   </div>
 </div>
 
+<script>
+  window.va = window.va || function () { (window.vaq = window.vaq || []).push(arguments); };
+</script>
+<script defer src="/_vercel/insights/script.js"></script>
 </body>
 </html>