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/pause_plugin.rs

@@ -21,7 +21,7 @@
 //! active opens the overlay as normal.
 
 use bevy::prelude::*;
-use solitaire_core::game_state::DrawMode;
+use solitaire_core::DrawMode;
 use solitaire_data::save_game_state_to;
 
 use crate::events::{
@@ -965,7 +965,7 @@ mod tests {
     /// Provides a fresh `GameStateResource` (not won) so the modal can
     /// open. `move_count` doesn't matter — the gate is just `!is_won`.
     fn forfeit_app() -> App {
-        use solitaire_core::game_state::{DrawMode, GameState};
+        use solitaire_core::{DrawMode, game_state::GameState};
         let mut app = App::new();
         app.add_plugins(MinimalPlugins).add_plugins(PausePlugin);
         app.init_resource::<ButtonInput<KeyCode>>();
@@ -1020,7 +1020,7 @@ mod tests {
     /// hotkey was received but is currently a no-op.
     #[test]
     fn forfeit_request_emits_toast_and_skips_modal_when_game_is_won() {
-        use solitaire_core::game_state::{DrawMode, GameState};
+        use solitaire_core::{DrawMode, game_state::GameState};
         let mut app = App::new();
         app.add_plugins(MinimalPlugins).add_plugins(PausePlugin);
         app.init_resource::<ButtonInput<KeyCode>>();