refactor(core): move solver to solitaire_data, DrawMode to klondike_adapter, remove pile/solver/schema_version

- Delete solitaire_core::solver — moved wholesale to solitaire_data::solver (re-exported at crate root)
- Delete solitaire_core::pile — no external users
- Move DrawMode from game_state to klondike_adapter; re-export as solitaire_core::DrawMode
- Remove schema_version field from GameState (redundant — deserializer stamps it from the constant)
- Update all callers across solitaire_data, solitaire_engine, solitaire_assetgen, solitaire_wasm

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_assetgen/src/bin/gen_difficulty_seeds.rs

@@ -19,8 +19,8 @@
 //!   --per-tier  Seeds to emit per tier (default 40)
 //!   --help      Print this message
 
-use solitaire_core::game_state::DrawMode;
-use solitaire_core::solver::{SolverConfig, SolverResult, try_solve};
+use solitaire_core::DrawMode;
+use solitaire_data::solver::{SolverConfig, SolverResult, try_solve};
 
 // Budget boundaries defining each tier. A seed belongs to the lowest tier
 // whose budget proves it Winnable.

solitaire_assetgen/src/bin/gen_seeds.rs

@@ -17,8 +17,8 @@
 //!   --count  Number of Winnable seeds to emit (default 75)
 //!   --help   Print this message
 
-use solitaire_core::game_state::DrawMode;
-use solitaire_core::solver::{SolverConfig, SolverResult, try_solve};
+use solitaire_core::DrawMode;
+use solitaire_data::solver::{SolverConfig, SolverResult, try_solve};
 
 fn main() {
     let mut args = std::env::args().skip(1).peekable();