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/weekly_goals_plugin.rs

@@ -82,7 +82,7 @@ fn evaluate_weekly_goals(
     for ev in events.drain(..) {
         let ctx = WeeklyGoalContext {
             time_seconds: ev.time_seconds,
-            used_undo: game.0.undo_count > 0,
+            used_undo: game.0.undo_count() > 0,
             draw_mode: game.0.draw_mode(),
         };
         for def in WEEKLY_GOALS {
@@ -177,7 +177,7 @@ mod tests {
         app.world_mut()
             .resource_mut::<GameStateResource>()
             .0
-            .undo_count = 1;
+            .force_test_undos(1);
 
         app.world_mut().write_message(GameWonEvent {
             score: 500,