fix: null display name, settings scrollbar, redundant passkey offer

- Profile API returns empty string instead of "null" when Logto user
  has no display name set (String.valueOf(null) → "null" bug).
- SettingsPage: add overflowY auto + flex 1 so content scrolls within
  the AppShell layout (which uses overflow: hidden).
- Remove redundant passkey offer from onboarding page — passkey
  enrollment now happens during sign-in via the Experience API.

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

src/main/java/net/siegeln/cameleer/saas/account/AccountService.java

@@ -46,10 +46,12 @@ public class AccountService {
         if (user == null) {
             throw new ResponseStatusException(HttpStatus.NOT_FOUND, "User not found");
         }
+        Object nameVal = user.get("name");
+        Object emailVal = user.get("primaryEmail");
         return new ProfileData(
                 userId,
-                String.valueOf(user.getOrDefault("name", "")),
-                String.valueOf(user.getOrDefault("primaryEmail", ""))
+                nameVal != null ? String.valueOf(nameVal) : "",
+                emailVal != null ? String.valueOf(emailVal) : ""
         );
     }