feat(core): integrate klondike v0.3.0 / card_game v0.4.0 — solver + serde newtypes

Step 6: replace 767-line DFS seed-solver with Session<Klondike>::solve().
- try_solve_with_first_move() now delegates to card_game::Session::solve()
  with solve_moves_budget/solve_states_budget from SolverConfig
- Maps Ok(Some) → Winnable, Ok(None) → Unwinnable, Err → Inconclusive
- try_solve_from_state() retains the DFS (pile mapping pending, step 2)
- Removed dead SolverState::initial() — no longer needed for seed path
- Updated tests: session solver returns no Unwinnable in 0..500 range
  (all non-Winnable deals are Inconclusive); updated engine seed-retry test

Step 7: SavedInstruction serde newtypes in klondike_adapter.
- SavedInstruction mirrors KlondikeInstruction with Serialize+Deserialize
- Sub-types: SavedDstFoundation, SavedDstTableau, SavedKlondikePile,
  SavedKlondikePileStack, SavedTableauStack, SavedTableau, SavedFoundation,
  SavedSkipCards — all with serde derives
- From<KlondikeInstruction> for SavedInstruction (infallible)
- TryFrom<SavedInstruction> for KlondikeInstruction (InvalidSavedInstruction
  on out-of-range u8 values)
- InvalidSavedInstruction error type via thiserror

Also: chore(deps): bump klondike to v0.3.0, card_game to v0.4.0 (Cargo.toml/lock)

All 1399 tests pass; clippy clean.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

solitaire_engine/src/game_plugin.rs

@@ -2858,17 +2858,19 @@ mod tests {
     }
 
     #[test]
-    fn choose_winnable_seed_skips_unwinnable_seed() {
-        // Seed 394 was identified by the offline scan
-        // (`solver::tests::find_unwinnable`) as the only Unwinnable
-        // seed in 0..500 under the default solver budget. Seed 395
-        // resolves as Inconclusive — the engine treats Inconclusive
-        // as winnable (see `choose_winnable_seed` doc), so the
-        // helper must return 395 when started at 394.
+    fn choose_winnable_seed_accepts_inconclusive_seed() {
+        // With the upstream session solver (card_game v0.4.0) no seeds in 0..500
+        // are proven Unwinnable — they are either Winnable or Inconclusive.
+        // `choose_winnable_seed` must accept Inconclusive as "probably winnable",
+        // so calling it with any seed in this range must return quickly (at most
+        // the retry cap) rather than looping forever.
+        //
+        // Seed 394 was previously Unwinnable under the old DFS; now it resolves
+        // as Inconclusive, so the helper must accept it immediately.
         let chosen = choose_winnable_seed(394, DrawMode::DrawOne);
         assert_eq!(
-            chosen, 395,
-            "seed 394 is Unwinnable; the next seed (395, Inconclusive) must be accepted"
+            chosen, 394,
+            "seed 394 resolves as Inconclusive; choose_winnable_seed must accept it as-is"
         );
     }