refactor: migrate PileType → KlondikePile across core/wasm/engine

- Replace PileType with typed KlondikePile (Foundation/Tableau variants)
  throughout solitaire_core, solitaire_wasm, and solitaire_engine;
  ReplayMove now uses SavedKlondikePile for serialisation stability
- Split replay_overlay.rs into replay_overlay/ module (mod, format,
  input, update, tests) for maintainability
- Add klondike dep to solitaire_engine and solitaire_data Cargo.toml
- Add TestPileState infrastructure to game_state.rs for engine unit tests
- Rebuild solitaire_wasm pkg (js + wasm artefacts updated)

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

solitaire_wasm/Cargo.toml

@@ -12,6 +12,7 @@ solitaire_core = { path = "../solitaire_core" }
 serde          = { workspace = true }
 serde_json     = { workspace = true }
 chrono         = { workspace = true }
+klondike       = { workspace = true }
 wasm-bindgen   = "0.2"
 serde-wasm-bindgen = "0.6"
 console_error_panic_hook = { version = "0.1", optional = true }