style: cargo fmt under rustfmt 1.9 and gate formatting in CI

The repo was formatted under an older stable; rustfmt 1.9 (Rust 1.95)
wraps signatures and call sites differently, so every touched file was
picking up unrelated formatting hunks. One mechanical pass, and a
'cargo fmt --check' step in the test workflow (same pinned 1.95.0
toolchain) so drift can't accumulate again.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

solitaire_engine/src/events.rs

@@ -2,8 +2,8 @@
 
 use bevy::prelude::Message;
 use solitaire_core::KlondikePile;
-use solitaire_core::{Card, Suit};
 use solitaire_core::game_state::GameMode;
+use solitaire_core::{Card, Suit};
 use solitaire_data::AchievementRecord;
 use solitaire_sync::SyncResponse;