Support ultrawide layout with equal columns and taiji branding.

Use 50/50 mode workspace columns, widen content to 1920px on fish screens, replace header logo with taiji icon, and add full-page taiji backdrop.

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

components/page-shell.tsx

@@ -1,5 +1,6 @@
 import Header from "@/components/header";
 import Footer from "@/components/footer";
+import TaijiBackdrop from "@/components/layout/taiji-backdrop";
 
 export default function PageShell({
   children,
@@ -9,11 +10,10 @@ export default function PageShell({
   className?: string;
 }) {
   return (
-    <div className="flex min-h-screen flex-col">
+    <div className="relative flex min-h-screen flex-col">
+      <TaijiBackdrop />
       <Header />
-      <div className={`mx-auto flex w-full flex-1 flex-col ${className}`}>
-        {children}
-      </div>
+      <div className={`flex w-full flex-1 flex-col ${className}`}>{children}</div>
       <Footer />
     </div>
   );