refactor(core): derive Copy for DrawMode; drop redundant .clone() calls (M-18)

DrawMode is a fieldless two-variant enum — it is trivially bitwise-
copyable. Adding Copy + updating choose_winnable_seed to take the value
directly eliminates 13 superfluous .clone() calls across solitaire_core,
solitaire_engine, solitaire_assetgen, and solitaire_wasm.

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

solitaire_core/src/game_state.rs

@@ -43,7 +43,7 @@ mod pile_map_serde {
 }
 
 /// Whether cards are drawn one at a time or three at a time from the stock.
-#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
 pub enum DrawMode {
     /// Draw one card from stock per turn.
     DrawOne,

solitaire_core/src/solver.rs

@@ -665,7 +665,7 @@ impl SolverState {
             foundation,
             stock,
             waste,
-            draw_mode: game.draw_mode.clone(),
+            draw_mode: game.draw_mode,
             just_drew: false,
             consecutive_draws: 0,
         }