refactor(core): derive draw_mode/is_won/move_count/is_auto_completable from session

Remove the draw_mode, move_count, is_won, and is_auto_completable fields
from GameState; they are now &self methods deriving from the underlying
card_game session (draw_mode from session config, move_count from history
length, is_won/is_auto_completable from check_win/check_auto_complete).

Tests previously fabricated these via direct field writes, which is no
longer possible. Add gated test-support overrides on TestPileState
(won/auto_completable/move_count) plus setters set_test_won,
set_test_auto_completable, set_test_move_count, and set_test_draw_mode
(re-deals the seed). All compiled out in production builds.

Fix the field->method ripple across solitaire_data, solitaire_wasm, and
solitaire_engine. Add a test-support dev-dependency to solitaire_data for
the won-game storage test.

cargo test --workspace and cargo clippy --workspace -- -D warnings pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

solitaire_core/src/proptest_tests.rs

@@ -89,7 +89,7 @@ fn apply_random_actions(game: &mut GameState, actions: &[(bool, usize)]) {
 /// available), using `move_idx` to select among the legal options.
 /// Returns `true` when a move was successfully applied.
 fn apply_one_move(game: &mut GameState, move_idx: usize) -> bool {
-    if game.is_won {
+    if game.is_won() {
         return false;
     }
     let instructions = game.possible_instructions();
@@ -218,10 +218,10 @@ proptest! {
 
         // Snapshot the state before the move.
         let before_ids = all_cards(&game);
-        let before_move_count = game.move_count;
+        let before_move_count = game.move_count();
 
         // Apply one move.
-        if !apply_one_move(&mut game, move_idx) || game.is_won {
+        if !apply_one_move(&mut game, move_idx) || game.is_won() {
             return Ok(()); // nothing to undo
         }
 
@@ -236,7 +236,7 @@ proptest! {
             "pile layout after undo differs from the pre-move snapshot",
         );
         prop_assert_eq!(
-            game.move_count,
+            game.move_count(),
             before_move_count,
             "move_count after undo must equal the pre-move value",
         );