style: move page gradient to global background so it shows behind header

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/frontend/src/routes/+layout.svelte

@@ -28,7 +28,9 @@
 
 <div class="bg-background text-foreground min-h-screen">
   <!-- Advanced Global Plasma Background -->
-  <div class="fixed inset-0 pointer-events-none overflow-hidden">
+  <div
+    class="fixed inset-0 pointer-events-none overflow-hidden bg-gradient-to-b from-primary/12 via-accent/6 to-transparent"
+  >
     <!-- Large primary blobs -->
     <div
       class="absolute -top-40 -left-40 w-80 h-80 bg-gradient-to-r from-primary/12 via-accent/18 to-primary/8 rounded-full blur-3xl animate-blob-ultra-slow"