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_assetgen/src/bin/gen_difficulty_seeds.rs

@@ -20,7 +20,7 @@
 //!   --help      Print this message
 
 use solitaire_core::DrawMode;
-use solitaire_data::solver::try_solve;
+use solitaire_core::game_state::GameState;
 
 // Budget boundaries defining each tier. A seed belongs to the lowest tier
 // whose budget proves it Winnable.
@@ -99,7 +99,7 @@ fn main() {
             if buckets[i].len() >= per_tier {
                 continue;
             }
-            match try_solve(seed, draw_mode, move_budget, state_budget) {
+            match GameState::solve_fresh_deal(seed, draw_mode, move_budget, state_budget) {
                 Ok(Some(_)) => {
                     buckets[i].push(seed);
                     eprintln!(

solitaire_assetgen/src/bin/gen_seeds.rs

@@ -18,7 +18,8 @@
 //!   --help   Print this message
 
 use solitaire_core::DrawMode;
-use solitaire_data::solver::{DEFAULT_SOLVE_MOVES_BUDGET, DEFAULT_SOLVE_STATES_BUDGET, try_solve};
+use solitaire_core::game_state::GameState;
+use solitaire_core::{DEFAULT_SOLVE_MOVES_BUDGET, DEFAULT_SOLVE_STATES_BUDGET};
 
 fn main() {
     let mut args = std::env::args().skip(1).peekable();
@@ -77,7 +78,7 @@ fn main() {
     while found.len() < count {
         tried += 1;
         if matches!(
-            try_solve(
+            GameState::solve_fresh_deal(
                 seed,
                 draw_mode,
                 DEFAULT_SOLVE_MOVES_BUDGET,