refactor: replace local DrawMode with upstream klondike::DrawStockConfig (#82)

DrawMode was a 1:1 mirror of klondike::DrawStockConfig (DrawOne/DrawThree).
Delete it and use the upstream type everywhere; re-export DrawStockConfig from
solitaire_core. config_for assigns draw_stock directly and draw_mode() returns
session.config().inner.draw_stock.

Serde is unchanged — DrawStockConfig serialises to the same "DrawOne"/"DrawThree"
named variants, so persisted game_state.json / replay JSON stay byte-compatible
(no migration). Field/method/variable names containing draw_mode are unchanged.

35 files, mechanical type swap across all crates. Implemented via a multi-agent
workflow (core → per-crate consumers → verify). cargo test --workspace and
clippy --workspace --all-targets -- -D warnings green.

Closes #82

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

solitaire_assetgen/src/bin/gen_seeds.rs

@@ -17,7 +17,7 @@
 //!   --count  Number of Winnable seeds to emit (default 75)
 //!   --help   Print this message
 
-use solitaire_core::DrawMode;
+use solitaire_core::DrawStockConfig;
 use solitaire_core::game_state::GameState;
 use solitaire_core::{DEFAULT_SOLVE_MOVES_BUDGET, DEFAULT_SOLVE_STATES_BUDGET};
 
@@ -68,7 +68,7 @@ fn main() {
         std::process::exit(1);
     }
 
-    let draw_mode = DrawMode::DrawOne;
+    let draw_mode = DrawStockConfig::DrawOne;
     let mut found: Vec<u64> = Vec::with_capacity(count);
     let mut tried: u64 = 0;
     let mut seed = start;