fix(subscription): remove double-centering gap beside main nav

The page wrapped its grid in a second maxWidth:1180/margin:auto on top of the
shell's already-centered .content (max-width 1480), leaving a ~150px gap
between the settings menu and the main navigation. Make the page full-width so
the settings sidebar sits flush against the main nav; trim the sidebar column
to 248px to match the app nav width.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

assets/admin/pages/SubscriptionPage.tsx

@@ -116,8 +116,8 @@ export default function SubscriptionPage() {
   };
 
   return (
-    <div className="fade-in" dir="rtl" style={{ maxWidth: 1180, margin: '0 auto' }}>
-      <div className="grid grid-cols-1 lg:grid-cols-[280px_minmax(0,1fr)] gap-5">
+    <div className="fade-in" dir="rtl" style={{ width: '100%' }}>
+      <div className="grid grid-cols-1 lg:grid-cols-[248px_minmax(0,1fr)] gap-5">
         <PurchaseSubscriptionSidebar active="subscription" />
 
         <div