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_wasm/src/lib.rs

@@ -119,7 +119,7 @@ impl ReplayPlayer {
         let replay: Replay =
             serde_json::from_str(replay_json).map_err(|e| format!("invalid replay JSON: {e}"))?;
         let game =
-            GameState::new_with_mode(replay.seed, replay.draw_mode.clone(), replay.mode);
+            GameState::new_with_mode(replay.seed, replay.draw_mode, replay.mode);
         Ok(Self {
             game,
             moves: replay.moves,