fix(data): enforce 32-char display_name limit at sync client boundary (M-22)

opt_in_leaderboard in sync_client.rs was passing display_name through
as-is, relying solely on the engine's .chars().take(32) call upstream.
Add the truncation in the sync client so any caller is protected, and
also apply it at save-time in handle_display_name_confirm so settings
never stores an over-length name.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_engine/src/leaderboard_plugin.rs

@@ -746,7 +746,7 @@ fn handle_display_name_confirm(
         return;
     }
     if let Some(mut settings) = settings {
-        let trimmed = buf.0.trim().to_string();
+        let trimmed: String = buf.0.trim().chars().take(32).collect();
         settings.0.leaderboard_display_name = if trimmed.is_empty() {
             None
         } else {