refactor: delete solitaire_data::solver wrapper; solve via card_game directly

Remove the standalone solver wrapper module. Its thin shaping — build a
solve-budgeted Session, run card_game::Session::solve(), extract the first
useful move — moves onto the domain type in solitaire_core as
GameState::solve_first_move() / GameState::solve_fresh_deal(), with the budget
consts and the SolveOutcome alias re-exported from solitaire_core.

Solving is deterministic, IO-free game logic, so core (which already owns
GameState and exposes session().solve()) is its correct home; solitaire_data is
the persistence/sync layer and never should have owned it.

Consumers now call the core API directly:
- engine: pending_hint (solve_first_move), game_plugin + play_by_seed_plugin
  (solve_fresh_deal), input_plugin (budget consts)
- assetgen: gen_seeds + gen_difficulty_seeds (solve_fresh_deal)

The solver tests move to solitaire_core. cargo test --workspace and
clippy --workspace --all-targets -- -D warnings both green.

Resolves the "delete the solver" directive — card_game provides the solver.

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

solitaire_core/src/lib.rs

@@ -12,9 +12,13 @@ pub mod klondike_adapter;
 // 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 card_game::{Card, Session, SolveError};
 pub use klondike::{Foundation, Klondike, KlondikeInstruction, KlondikePile, Tableau};
 pub use klondike_adapter::DrawMode;
 
+// Solvability check API (delegates to `card_game::Session::solve`); replaces the
+// former `solitaire_data::solver` wrapper module.
+pub use game_state::{DEFAULT_SOLVE_MOVES_BUDGET, DEFAULT_SOLVE_STATES_BUDGET, SolveOutcome};
+
 #[cfg(test)]
 mod proptest_tests;