fix create deck issue

src/routes/CreateDeck.svelte

@@ -131,17 +131,23 @@
   }
 </script>
 
-<div class="page">
-  <header class="page-header">
-    <h1>Create deck</h1>
+<header class="page-header page-header-fixed">
+  <div class="page-header-inner">
+    <h1 class="page-header-title">Create deck</h1>
     <div class="header-actions">
-      <button type="button" class="btn btn-secondary" onclick={cancel} disabled={saving}>Cancel</button>
-      <button type="button" class="btn btn-primary" onclick={save} disabled={saving}>
-        {saving ? 'Saving…' : 'Save deck'}
-      </button>
+      {#if view === 'loading'}
+        <span class="header-spinner" aria-hidden="true"></span>
+      {:else}
+        <button type="button" class="btn btn-secondary" onclick={cancel} disabled={saving}>Cancel</button>
+        <button type="button" class="btn btn-primary" onclick={save} disabled={saving}>
+          {saving ? 'Saving…' : 'Save deck'}
+        </button>
+      {/if}
     </div>
-  </header>
+  </div>
+</header>
 
+<div class="page page-with-fixed-header">
   {#if view === 'loading'}
     <p class="auth-required">Loading…</p>
   {:else if view === 'signin'}
@@ -195,16 +201,33 @@
     margin: 0 auto;
   }
 
-  .page-header {
+  .page-with-fixed-header {
+    padding-top: calc(var(--navbar-height, 60px) + 3.5rem);
+  }
+
+  .page-header-fixed {
+    position: fixed;
+    top: var(--navbar-height, 60px);
+    left: 0;
+    right: 0;
+    z-index: 50;
+    background: var(--bg, #0f0f0f);
+    border-bottom: 1px solid var(--border, #333);
+    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.3);
+  }
+
+  .page-header-inner {
+    max-width: 700px;
+    margin: 0 auto;
+    padding: 0.75rem 1.5rem;
     display: flex;
     align-items: center;
     justify-content: space-between;
     flex-wrap: wrap;
     gap: 1rem;
-    margin-bottom: 1.5rem;
   }
 
-  .page-header h1 {
+  .page-header-title {
     margin: 0;
     font-size: 1.5rem;
     font-weight: 600;
@@ -214,6 +237,23 @@
   .header-actions {
     display: flex;
     gap: 0.5rem;
+    align-items: center;
+  }
+
+  .header-spinner {
+    display: inline-block;
+    width: 1.25rem;
+    height: 1.25rem;
+    border: 2px solid var(--border, #333);
+    border-top-color: var(--text-primary, #f0f0f0);
+    border-radius: 50%;
+    animation: header-spin 0.7s linear infinite;
+  }
+
+  @keyframes header-spin {
+    to {
+      transform: rotate(360deg);
+    }
   }
 
   .auth-required {