refactor(core): make KlondikeInstruction the move currency

Remove the (from, to, count) tuple as an internal move-passing wrapper.
Game logic now stays in KlondikeInstruction space end to end:

- Add GameState::apply_instruction, the native apply path. move_cards
  becomes a thin pile-coordinate adapter that converts to an instruction
  and delegates, so move bookkeeping (validation, score/recycle history,
  undo snapshot) lives in one place instead of being duplicated.
- next_auto_complete_move matches DstFoundation directly instead of
  projecting every candidate to pile coordinates.
- proptests and the storage round-trip test apply instructions directly
  rather than round-tripping instruction -> tuple -> move_cards.

The single instruction -> pile decode is renamed instruction_to_highlight
-> instruction_to_piles and kept in core: decoding a tableau run length
needs upstream pile-stack types core does not re-export, so relocating it
would duplicate the logic across engine and wasm. The two rendering edges
(engine hint highlight, wasm debug move list) call this one decoder; the
engine's hint_piles is a thin delegation to it.

Also includes the CardEntityIndex render-side index and a SelectionPlugin
init_resource fix so update_selection_highlight no longer panics in test
harnesses that omit CardPlugin.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

solitaire_core/src/lib.rs

@@ -8,9 +8,10 @@ pub mod klondike_adapter;
 // downstream crates (engine, wasm) can import from one place without a direct
 // `klondike` / `card_game` dep.
 //
-// `KlondikePileStack`, `SkipCards`, and `TableauStack` are intentionally NOT
-// re-exported — they are only used internally in `klondike_adapter.rs` and do
-// not appear in any public method signature.
+// `KlondikePileStack`, `SkipCards` and `TableauStack` are intentionally NOT
+// re-exported — they are only used internally (in `klondike_adapter.rs` and
+// when decoding instructions to piles in `instruction_to_piles`) and do not
+// appear in any public method signature.
 pub use card_game::{Card, Session};
 pub use klondike::{Foundation, Klondike, KlondikeInstruction, KlondikePile, Tableau};
 pub use klondike_adapter::DrawMode;