refactor(core): integrate card_game/klondike deps cleanly

Wire card_game 0.4.0 and klondike 0.3.0 as workspace deps in
solitaire_core and clean the integration seam across five areas:

- Move From<card_game::Suit/Rank> bridge impls out of card.rs and into
  klondike_adapter.rs so the product-type module is upstream-dep-free
- Add `use crate::card` alias to adapter; rename card_from_kl parameter
  to avoid shadowing; correct score_for_undo doc (it is Ferrous policy,
  not an upstream default — the solver explicitly passes undo_penalty=0)
- Mark Pile as a read-only projection / data-transfer type in its doc
  comment so game logic isn't accidentally routed through it
- Add GameState::session() read accessor exposing the underlying
  Session<Klondike> for replay history and solver use by external crates;
  update solver.rs to use the accessor instead of the pub(crate) field
- Re-export Foundation, Klondike, KlondikePile, Session, Tableau from
  solitaire_core::lib so downstream crates (engine, wasm) can import
  from one place without a direct klondike/card_game dep
- Add proptest property tests: card conservation (52 unique IDs always
  present), deal determinism, undo pile-layout invariant, legal moves
  always succeed

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_core/Cargo.toml

@@ -8,6 +8,9 @@ edition.workspace = true
 default = []
 test-support = []
 
+[dev-dependencies]
+proptest = "1"
+
 [dependencies]
 serde     = { workspace = true }
 thiserror = { workspace = true }