feat: add public leaderboards with opt-out privacy setting

apps/web/src/components/game/EditProfileModal.tsx

@@ -179,6 +179,21 @@ export const EditProfileModal = ({ onClose }: EditProfileModalProps): React.JSX.
               </div>
             </div>
 
+            <div className="edit-profile-section">
+              <p className="edit-profile-label">Privacy</p>
+              <p className="edit-profile-sublabel">Control your visibility on public leaderboards.</p>
+              <button
+                className={`stat-toggle-btn ${settings.showOnLeaderboards ? "stat-toggle-on" : "stat-toggle-off"}`}
+                onClick={() => { toggleSetting("showOnLeaderboards"); }}
+                type="button"
+              >
+                <span>🏆 Appear on Leaderboards</span>
+                <span className="stat-toggle-indicator">
+                  {settings.showOnLeaderboards ? "✓ Shown" : "Hidden"}
+                </span>
+              </button>
+            </div>
+
             <div className="edit-profile-section">
               <p className="edit-profile-label">Number Format</p>
               <p className="edit-profile-sublabel">How large numbers appear across the game.</p>