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_engine/src/sync_plugin.rs

@@ -322,7 +322,7 @@ fn push_replay_on_win(
         }
         let replay = Replay::new(
             game.0.seed,
-            game.0.draw_mode.clone(),
+            game.0.draw_mode,
             game.0.mode,
             ev.time_seconds,
             ev.score,