fix: add overflow-x:hidden to html to stop blob-caused layout shaking

Animated blobs with translate+scale overflow their containers,
causing horizontal scrollbar to flicker and page to jitter.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/index.css

@@ -62,8 +62,8 @@
 }
 
 @layer base {
-  /* Thin overlay scrollbar — doesn't consume layout space */
   html {
+    overflow-x: hidden;
     scrollbar-width: thin;
     scrollbar-color: rgba(0,0,0,0.15) transparent;
   }