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_engine/src/pending_hint.rs

@@ -63,7 +63,7 @@ impl PendingHintTask {
     /// Spawn a new solver task for `state` with `config`. Drops any
     /// previously in-flight task first (cancel-on-replace).
     pub fn spawn(&mut self, state: GameState, config: SolverConfig) {
-        let move_count_at_spawn = state.move_count;
+        let move_count_at_spawn = state.move_count();
         let handle = AsyncComputeTaskPool::get().spawn(async move {
             let outcome = try_solve_from_state(&state, &config);
             match outcome.result {
@@ -156,7 +156,7 @@ pub fn poll_pending_hint_task(
     pending.inner = None;
 
     let Some(g) = game else { return };
-    if g.0.move_count != move_count_at_spawn {
+    if g.0.move_count() != move_count_at_spawn {
         return;
     }