style: increase max-width container constraint across admin pages to 6xl

app/admin/backend/page.tsx

@@ -32,7 +32,7 @@ export default async function BackendPage() {
 
   return (
     <AdminShell>
-      <div className="p-6 space-y-6 max-w-4xl mx-auto w-full">
+      <div className="p-6 space-y-6 max-w-6xl mx-auto w-full">
         <div>
           <h1 className="text-3xl font-bold tracking-tight">Backend</h1>
           <p className="text-muted-foreground mt-1">

app/admin/form/[id]/extra/page.tsx

@@ -19,7 +19,7 @@ export default async function AdminExtraPage(
   }
 
   return (
-    <div className="space-y-6 max-w-4xl mx-auto pb-12">
+    <div className="space-y-6 w-full max-w-6xl mx-auto pb-12">
       <div className="flex items-center justify-between">
         <div>
           <h1 className="text-3xl font-bold tracking-tight">Extra Settings</h1>

app/admin/form/[id]/page.tsx

@@ -25,7 +25,7 @@ export default async function AdminDashboardPage(
   });
 
   return (
-    <div className="space-y-6 max-w-4xl mx-auto pb-12">
+    <div className="space-y-6 w-full max-w-6xl mx-auto pb-12">
       <div className="flex items-center justify-between">
         <div>
           <h1 className="text-3xl font-bold tracking-tight">Edit Form</h1>

app/admin/form/[id]/result/[submissionId]/page.tsx

@@ -47,7 +47,7 @@ export default async function SubmissionDetailPage({ params }: SubmissionDetailP
   const nextId = currentIndex >= 0 && currentIndex < submissionsList.length - 1 ? submissionsList[currentIndex + 1].id : null;
 
   return (
-    <div className="space-y-6 w-full max-w-4xl mx-auto p-4 md:p-6 pb-10">
+    <div className="space-y-6 w-full max-w-6xl mx-auto p-4 md:p-6 pb-10">
       <div className="flex items-center justify-between">
         <div className="flex items-center gap-2">
           <Link href={`/admin/form/${formId}/result`}>

app/admin/form/[id]/result/page.tsx

@@ -20,7 +20,7 @@ export default async function ResultsListPage(
   });
 
   return (
-    <div className="space-y-6 w-full max-w-4xl mx-auto p-4 md:p-6">
+    <div className="space-y-6 w-full max-w-6xl mx-auto p-4 md:p-6">
       <div>
         <Button variant="ghost" asChild className="mb-4">
           <Link href={`/admin/form/${params.id}`}>

app/admin/page.tsx

@@ -11,7 +11,7 @@ import { ClipboardList, Server } from "lucide-react";
 export default function AdminPage() {
   return (
     <AdminShell>
-      <div className="p-6 space-y-6 max-w-4xl mx-auto w-full">
+      <div className="p-6 space-y-6 max-w-6xl mx-auto w-full">
         <div>
           <h1 className="text-3xl font-bold tracking-tight">Dashboard</h1>
           <p className="text-muted-foreground mt-1">Admin control panel</p>