fix(engine): add missing A/L/O shortcuts to help screen overlay

The help overlay only listed S and H; added Achievements (A),
Leaderboard (L), and Settings (O) which were already implemented
but undocumented in the cheat sheet.

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

solitaire_engine/src/help_plugin.rs

@@ -51,8 +51,11 @@ fn spawn_help_screen(commands: &mut Commands) {
         "  T            Start a Time Attack session (level 5+)".to_string(),
         String::new(),
         "-- Overlays --".to_string(),
-        "  S            Toggle stats / progression".to_string(),
-        "  H or ?       Toggle this help".to_string(),
+        "  S            Stats & progression".to_string(),
+        "  A            Achievements".to_string(),
+        "  L            Leaderboard".to_string(),
+        "  O            Settings".to_string(),
+        "  H or ?       This help screen".to_string(),
         "  Esc          Pause / resume".to_string(),
         "  [ / ]        SFX volume down / up".to_string(),
         String::new(),