Apply 1400px max width to all admin pages

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/src/routes/admin/categories/+page.svelte

@@ -70,7 +70,7 @@
   }
 </script>
 
-<div class="h-full flex flex-col">
+<div class="h-full flex flex-col max-w-[1400px] mx-auto w-full">
   <div class="flex-shrink-0 border-b border-surface-border px-6 py-3">
     <h1 class="text-sm font-semibold text-text-primary">Categories & Groups</h1>
   </div>

src/client/src/routes/admin/stores/[id]/+page.svelte

@@ -44,7 +44,7 @@
   }
 </script>
 
-<div class="h-full flex flex-col">
+<div class="h-full flex flex-col max-w-[1400px] mx-auto w-full">
   <div class="flex-shrink-0 border-b border-surface-border px-6 py-3 flex items-center justify-between">
     <div class="flex items-center gap-3">
       <a href="/admin" class="text-text-tertiary hover:text-text-secondary transition-colors">&larr;</a>

src/client/src/routes/admin/stores/[id]/test/+page.svelte

@@ -31,7 +31,7 @@
   }
 </script>
 
-<div class="h-full flex flex-col">
+<div class="h-full flex flex-col max-w-[1400px] mx-auto w-full">
   {#if loading}
     <div class="p-6 animate-pulse">
       <div class="bg-surface-raised h-8 w-48 rounded mb-4"></div>

src/client/src/routes/admin/stores/new/+page.svelte

@@ -34,7 +34,7 @@
   }
 </script>
 
-<div class="h-full flex flex-col">
+<div class="h-full flex flex-col max-w-[1400px] mx-auto w-full">
   <div class="flex-shrink-0 border-b border-surface-border px-6 py-3 flex items-center justify-between">
     <div class="flex items-center gap-3">
       <a href="/admin" class="text-text-tertiary hover:text-text-secondary transition-colors">&larr;</a>