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/hud_plugin/mod.rs

@@ -19,7 +19,6 @@ use interaction::*;
 use spawn::*;
 use updates::*;
 
-
 // On wasm32 AvatarPlugin is gated out; define a placeholder type so the
 // Option<Res<AvatarResource>> parameters below compile without changes.
 // The resource is never inserted on wasm, so every call resolves to None.