feat(core): add pile, error, deck, rules, scoring modules with tests

Implements PileType/Pile, MoveError (thiserror), Deck with seeded shuffle,
deal_klondike layout, foundation/tableau placement rules, and Windows XP
Standard scoring — 41 tests, clippy clean.

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

solitaire_core/src/pile.rs

@@ -0,0 +1,70 @@
+use serde::{Deserialize, Serialize};
+use crate::card::{Card, Suit};
+
+/// Identifies which pile on the board a set of cards belongs to.
+#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum PileType {
+    /// The face-down draw pile.
+    Stock,
+    /// The face-up discard pile drawn to.
+    Waste,
+    /// One of the four suit-ordered foundation piles.
+    Foundation(Suit),
+    /// One of the seven tableau columns (0–6).
+    Tableau(usize),
+}
+
+/// A named collection of cards in a specific board position.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Pile {
+    pub pile_type: PileType,
+    pub cards: Vec<Card>,
+}
+
+impl Pile {
+    /// Creates a new empty pile of the given type.
+    pub fn new(pile_type: PileType) -> Self {
+        Self { pile_type, cards: Vec::new() }
+    }
+
+    /// Returns a reference to the top (last) card, or `None` if empty.
+    pub fn top(&self) -> Option<&Card> {
+        self.cards.last()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::card::{Card, Rank, Suit};
+
+    #[test]
+    fn new_pile_is_empty() {
+        let pile = Pile::new(PileType::Stock);
+        assert!(pile.cards.is_empty());
+    }
+
+    #[test]
+    fn pile_top_returns_last_card() {
+        let mut pile = Pile::new(PileType::Waste);
+        pile.cards.push(Card { id: 0, suit: Suit::Hearts, rank: Rank::Ace, face_up: true });
+        pile.cards.push(Card { id: 1, suit: Suit::Clubs, rank: Rank::Two, face_up: true });
+        assert_eq!(pile.top().unwrap().id, 1);
+    }
+
+    #[test]
+    fn pile_top_on_empty_is_none() {
+        let pile = Pile::new(PileType::Waste);
+        assert!(pile.top().is_none());
+    }
+
+    #[test]
+    fn pile_type_foundation_uses_suit() {
+        assert_ne!(PileType::Foundation(Suit::Hearts), PileType::Foundation(Suit::Spades));
+    }
+
+    #[test]
+    fn pile_type_tableau_uses_index() {
+        assert_ne!(PileType::Tableau(0), PileType::Tableau(6));
+    }
+}