fix(ui): add wrapper div to prevent content from appearing under nav

Added outer wrapper div with minHeight and background color to match
the pattern used by other pages (flashcards, calendar). This ensures
content doesn't appear under the fixed navigation bar.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

apps/web/src/app/create/abacus/page.tsx

@@ -75,14 +75,15 @@ export default function ThreeDPrintPage() {
 
   return (
     <PageWithNav navTitle={t('navTitle')} navEmoji="🖨️">
-      <div
-        data-component="3d-print-page"
-        className={css({
-          maxWidth: '1200px',
-          mx: 'auto',
-          p: 6,
-        })}
-      >
+      <div className={css({ minHeight: '100vh', bg: 'gray.50' })}>
+        <div
+          data-component="3d-print-page"
+          className={css({
+            maxWidth: '1200px',
+            mx: 'auto',
+            p: 6,
+          })}
+        >
         <h1
           className={css({
             fontSize: '3xl',
@@ -562,7 +563,7 @@ export default function ThreeDPrintPage() {
           </div>
         </div>
       </div>
-    </div>
+      </div>
     </PageWithNav>
   )
 }