refactor(core): move solver to solitaire_data, DrawMode to klondike_adapter, remove pile/solver/schema_version

- Delete solitaire_core::solver — moved wholesale to solitaire_data::solver (re-exported at crate root)
- Delete solitaire_core::pile — no external users
- Move DrawMode from game_state to klondike_adapter; re-export as solitaire_core::DrawMode
- Remove schema_version field from GameState (redundant — deserializer stamps it from the constant)
- Update all callers across solitaire_data, solitaire_engine, solitaire_assetgen, solitaire_wasm

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

solitaire_engine/src/win_summary_plugin.rs

@@ -1210,7 +1210,7 @@ mod tests {
             .insert_resource(StatsResource(StatsSnapshot::default()))
             .insert_resource(GameStateResource(GameState::new(
                 0,
-                solitaire_core::game_state::DrawMode::DrawOne,
+                solitaire_core::DrawMode::DrawOne,
             )))
             .insert_resource(ProgressResource(PlayerProgress::default()));
         app.update();
@@ -1539,7 +1539,7 @@ mod tests {
             .challenge_index = 4;
         // Switch game mode to Challenge.
         {
-            use solitaire_core::game_state::DrawMode;
+            use solitaire_core::DrawMode;
             app.world_mut().resource_mut::<GameStateResource>().0 =
                 GameState::new_with_mode(1, DrawMode::DrawOne, GameMode::Challenge);
         }
@@ -1585,7 +1585,7 @@ mod tests {
     /// mode-multiplier rows.
     #[test]
     fn cache_win_data_captures_undo_count_and_mode() {
-        use solitaire_core::game_state::DrawMode;
+        use solitaire_core::DrawMode;
 
         let mut app = make_app();
         // Set up a Zen-mode game with 2 undos used.