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/interaction.rs

@@ -3,8 +3,6 @@
 
 use super::*;
 
-
-
 /// `Changed<Interaction>` filter ensures we only react on the frame the
 /// interaction state transitions, avoiding repeat events while the button
 /// is held down. Each click handler fires the corresponding request event,
@@ -613,4 +611,3 @@ pub(super) fn toggle_hud_on_tap(
         }
     }
 }
-