Tighten ultrawide layout with visible side gutters.

Cap content at 768-960px via PageShell width tiers, add muted outer margins, and limit gua grid to four columns.

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

app/page.tsx

@@ -2,7 +2,6 @@ import Link from "next/link";
 import PageShell from "@/components/page-shell";
 import { BookOpen, BrainCircuit, Compass, Sparkles } from "lucide-react";
 import { ZenCard } from "@/components/ui/zen-card";
-import { HOME_CONTAINER } from "@/lib/layout";
 import { TaijiIcon } from "@/components/svg/taiji";
 
 const MODULES = [
@@ -38,7 +37,7 @@ const MODULES = [
 
 export default function Home() {
   return (
-    <PageShell className={`${HOME_CONTAINER} py-10 sm:py-14`}>
+    <PageShell width="narrow" className="py-10 sm:py-14">
       <div className="mb-10 text-center">
         <TaijiIcon className="mx-auto h-12 w-12 opacity-80" />
         <h1 className="mt-2 text-3xl font-bold tracking-[0.2em]">知命阁</h1>