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_data/Cargo.toml

@@ -16,6 +16,7 @@ dirs           = { workspace = true }
 reqwest        = { workspace = true }
 tokio          = { workspace = true }
 uuid           = { workspace = true }
+klondike       = { workspace = true }
 
 # `keyring-core` is the typed Entry/Error API used by
 # `auth_tokens`. The crate's own dependency tree pulls in