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_engine/src/pending_hint.rs

@@ -26,7 +26,6 @@ use bevy::prelude::*;
 use bevy::tasks::{AsyncComputeTaskPool, Task, futures_lite::future};
 use solitaire_core::KlondikeInstruction;
 use solitaire_core::game_state::GameState;
-use solitaire_data::solver::try_solve_from_state;
 
 use crate::card_plugin::CardEntity;
 use crate::events::{HintVisualEvent, InfoToastEvent, StateChangedEvent};
@@ -66,7 +65,7 @@ impl PendingHintTask {
             // Winnable (`Ok(Some)`) carries the first move on a winning path;
             // unwinnable (`Ok(None)`) and inconclusive (`Err`) both fall back
             // to the live-state heuristic so H always produces feedback.
-            match try_solve_from_state(&state, moves_budget, states_budget) {
+            match state.solve_first_move(moves_budget, states_budget) {
                 Ok(Some(first_move)) => HintTaskOutput::SolverMove(first_move),
                 Ok(None) | Err(_) => HintTaskOutput::NeedsHeuristic,
             }