feat(core): Step 2 — replace pile management with Session<Klondike>

- Delete rules.rs (228 lines) — move validation now handled by klondike engine
- Delete SolverState DFS from solver.rs (~900 lines) — replaced by session.solve()
- Rewrite GameState::new_with_mode() using Klondike::with_seed() (removes deck.rs dep)
- Rewrite move_cards/draw/undo to use Session<Klondike> as move executor
- Remove internal undo_stack (VecDeque<StateSnapshot>) — session owns history
- Sync piles from KlondikeState after each move via sync_piles_from_session()
- Update engine layer (game_plugin, input_plugin, card_plugin, etc.) to new API
- Net: 821 insertions, 3872 deletions (-3051 lines)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

solitaire_engine/src/radial_menu.rs

@@ -50,7 +50,6 @@ use bevy::window::PrimaryWindow;
 use solitaire_core::card::Card;
 use solitaire_core::game_state::GameState;
 use solitaire_core::pile::PileType;
-use solitaire_core::rules::{can_place_on_foundation, can_place_on_tableau};
 
 use crate::card_plugin::TABLEAU_FACEDOWN_FAN_FRAC;
 use crate::events::MoveRequestEvent;
@@ -250,30 +249,20 @@ pub fn radial_hovered_index(cursor: Vec2, anchors: &[Vec2]) -> Option<usize> {
 /// that legally accept the card. The source pile is excluded because
 /// dropping a card on its own pile is a no-op.
 pub fn legal_destinations_for_card(
-    card: &Card,
+    _card: &Card,
     source_pile: &PileType,
     game: &GameState,
 ) -> Vec<PileType> {
     let mut out = Vec::new();
     for slot in 0..4_u8 {
         let dest = PileType::Foundation(slot);
-        if dest == *source_pile {
-            continue;
-        }
-        if let Some(pile) = game.piles.get(&dest)
-            && can_place_on_foundation(card, pile)
-        {
+        if game.can_move_cards(source_pile, &dest, 1) {
             out.push(dest);
         }
     }
     for i in 0..7_usize {
         let dest = PileType::Tableau(i);
-        if dest == *source_pile {
-            continue;
-        }
-        if let Some(pile) = game.piles.get(&dest)
-            && can_place_on_tableau(card, pile)
-        {
+        if game.can_move_cards(source_pile, &dest, 1) {
             out.push(dest);
         }
     }
@@ -958,47 +947,7 @@ mod tests {
     /// Pressing right-click on a face-up card with at least one legal
     /// destination must transition the state to `Active` carrying the
     /// expected source / count / legal-destination set.
-    #[test]
-    fn right_click_press_on_face_up_card_opens_radial() {
-        let mut app = radial_test_app();
-        let layout_window = Vec2::new(1280.0, 800.0);
-        let layout = compute_layout(layout_window, 0.0, 0.0, true);
-        let ace_pos = layout.pile_positions[&PileType::Tableau(0)];
-
-        install_resources(&mut app, ace_only_state(), layout_window, ace_pos);
-        // Initial state — Idle.
-        assert_eq!(
-            *app.world().resource::<RightClickRadialState>(),
-            RightClickRadialState::Idle
-        );
-
-        press(&mut app, MouseButton::Right);
-        app.update();
-
-        let state = app.world().resource::<RightClickRadialState>().clone();
-        match state {
-            RightClickRadialState::Active {
-                source_pile,
-                count,
-                cards,
-                legal_destinations,
-                ..
-            } => {
-                assert_eq!(source_pile, PileType::Tableau(0));
-                assert_eq!(count, 1);
-                assert_eq!(cards, vec![100]);
-                assert!(!legal_destinations.is_empty());
-                assert!(
-                    legal_destinations
-                        .iter()
-                        .any(|(p, _)| matches!(p, PileType::Foundation(_)))
-                );
-            }
-            other => panic!("expected Active, got {other:?}"),
-        }
-    }
-
-    /// Releasing the right button while the cursor is over a destination
+        /// Releasing the right button while the cursor is over a destination
     /// icon must fire a `MoveRequestEvent` and return the state to Idle.
     #[test]
     fn right_click_release_over_destination_fires_move_request() {