fix(engine): resolve StatsUpdate system-set scheduling cycle

update_stats_on_new_game and handle_forfeit ran .before(GameMutation)
while being inside StatsUpdate.  win_summary_plugin constrains
cache_win_data.before(StatsUpdate), which forces the entire StatsUpdate
set to run after GameMutation — creating an unsolvable cycle that panicked
Bevy 0.18's schedule solver at startup.

Only update_stats_on_win (post-GameMutation) belongs in StatsUpdate.
The pre-GameMutation systems still run before GameMutation but outside
the set, so external .before(StatsUpdate)/.after(StatsUpdate) constraints
remain consistent.

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

solitaire_engine/src/stats_plugin.rs

@@ -82,12 +82,14 @@ impl Plugin for StatsPlugin {
             .add_message::<ForfeitEvent>()
             .add_message::<InfoToastEvent>()
             // record_abandoned must read `move_count` BEFORE handle_new_game
-            // clobbers it with a fresh game.
+            // clobbers it with a fresh game. These are NOT in StatsUpdate because
+            // StatsUpdate (as a set) is ordered after GameMutation by external
+            // constraints (win_summary_plugin: cache_win_data.before(StatsUpdate)),
+            // and a system cannot be both inside a set and individually before a
+            // set-level ordering constraint.
             .add_systems(
                 Update,
-                update_stats_on_new_game
+                update_stats_on_new_game.before(GameMutation),
-                    .before(GameMutation)
-                    .in_set(StatsUpdate),
             )
             .add_systems(
                 Update,
@@ -95,7 +97,7 @@ impl Plugin for StatsPlugin {
             )
             .add_systems(
                 Update,
-                handle_forfeit.before(GameMutation).in_set(StatsUpdate),
+                handle_forfeit.before(GameMutation),
             )
             .add_systems(Update, toggle_stats_screen.after(GameMutation));
     }