refactor(core): derive score/undo/recycle from upstream session stats

Replace the bespoke WXP scoring engine with the upstream
card_game/klondike session stats, eliminating duplicated state that
could drift from the single source of truth.

score()/undo_count()/recycle_count() now read session.stats(); the -15
undo penalty is configured as SessionConfig::undo_penalty and applied by
the upstream score formula. Save schema bumped v4 -> v5 (the three
counters are no longer persisted -- they are rebuilt by replaying the
forward instruction history on load).

- Remove GameState fields score, undo_count, recycle_count (#87)
- Remove score_history / is_recycle_history undo journal (#86)
- Remove KlondikeAdapter::apply_undo_score and the score_for_* helpers,
  plus pre_instruction_score_delta / will_flip_tableau_source (#84)

These three issues are a single atomic change: each removed field/helper
is consumed by the same draw/apply_instruction/undo/serde/PartialEq
paths, so they cannot compile or pass tests in isolation.

Behaviour changes (intentional): the escalating recycle penalty and
per-step score floor are gone (upstream linear scoring, floored once at
0); recycle_count is now cumulative; undo_count resets across save/load.

Refs #84, #86, #87

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

solitaire_engine/src/win_summary_plugin.rs

@@ -472,14 +472,14 @@ fn cache_win_data(
             None
         };
 
-        let used_undo = game.0.undo_count > 0;
+        let used_undo = game.0.undo_count() > 0;
         pending.score = ev.score;
         pending.time_seconds = ev.time_seconds;
         pending.xp = 0; // reset; XP event follows
         pending.xp_detail = build_xp_detail(ev.time_seconds, used_undo);
         pending.new_record = is_new_record;
         pending.challenge_level = challenge_level;
-        pending.undo_count = game.0.undo_count;
+        pending.undo_count = game.0.undo_count();
         pending.mode = game.0.mode;
 
         if is_new_record {
@@ -1587,7 +1587,7 @@ mod tests {
         {
             let mut game = app.world_mut().resource_mut::<GameStateResource>();
             game.0 = GameState::new_with_mode(7, DrawMode::DrawOne, GameMode::Zen);
-            game.0.undo_count = 2;
+            game.0.force_test_undos(2);
         }
 
         app.world_mut().write_message(GameWonEvent {