fix(ui): improve onboarding page styling to match sign-in page

Add 32px card padding and reduce max-width to 420px for consistency
with the sign-in page. Add noValidate to prevent browser-native
required validation outlines on inputs.

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

ui/src/pages/OnboardingPage.module.css

@@ -8,10 +8,14 @@
 
 .wrapper {
   width: 100%;
-  max-width: 480px;
+  max-width: 420px;
   padding: 16px;
 }
 
+.card {
+  padding: 32px;
+}
+
 .inner {
   display: flex;
   flex-direction: column;