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/ui_theme.rs

@@ -304,10 +304,7 @@ impl HighContrastBackground {
     /// [`BORDER_SUBTLE_HC`]. Currently used by the WIN MOVE scrub-bar
     /// marker which bumps `STATE_SUCCESS` → `STATE_SUCCESS_HC` rather
     /// than to a neutral gray.
-    pub const fn with_hc(
-        default_color: Color,
-        hc_color: Color,
-    ) -> Self {
+    pub const fn with_hc(default_color: Color, hc_color: Color) -> Self {
         Self {
             default_color,
             hc_color,