feat(accessibility): gate splash scanline + cursor pulse on reduce-motion

Resume-prompt Option E, part 1 of 2 (the reduce-motion piece;
HC chrome borders follow in a separate commit).

v0.21.1 wired `Settings::reduce_motion_mode` through
`effective_slide_secs` so cards snap instead of sliding under
reduce-motion. The design-system spec at §Accessibility (#3)
calls out two more sources of non-essential motion that
reduce-motion should suppress: the splash CRT scanline effect
and the splash cursor pulse. This commit gates both.

### Splash cursor pulse (`pulse_splash_cursor`)

Previously sine-pulsed every frame regardless of settings. Now
reads `Settings::reduce_motion_mode` and skips the pulse
multiplier when on — the cursor still fades in / out with the
global splash alpha (essential timing), but doesn't blink
(decorative motion). The fade is preserved on purpose: skipping
it would hard-cut the splash on/off, which is jarring; the spec
specifically calls out *non-essential* motion as the reduce-
motion target, and a decorative blink is more clearly
non-essential than a fade timeline.

### Splash scanline overlay (`spawn_splash`)

Previously generated and spawned unconditionally when
`Assets<Image>` was available. Now skipped entirely when
reduce-motion is on — without the scanline overlay the boot
screen still reads as terminal-themed (foreground content,
borders, palette swatches all unchanged); the scanlines are
purely decorative.

### Test

New `splash_skips_scanline_overlay_under_reduce_motion` pins
the gate behaviour: under `reduce_motion_mode = true`, the
splash root still spawns (essential motion intact) but the
`SplashScanlineOverlay` entity is absent. 1193 passing
(+1 from prior 1192).

Workspace clippy clean.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

solitaire_engine/src/splash_plugin.rs

@@ -219,12 +219,27 @@ fn spawn_splash(
 
     let font_handle = font_res.map(|f| f.0.clone()).unwrap_or_default();
 
+    // Settings is borrowed twice — once for the first_run_complete
+    // gate above, once here for the reduce-motion gate. The borrow
+    // above already happened (and was let-go via the `settings.as_deref()`
+    // pattern's auto-drop), so this re-read is safe.
+    let reduce_motion = settings.is_some_and(|s| s.0.reduce_motion_mode);
+
     // Generate the scanline texture handle up-front (when the asset
     // store is available — always true in production; opt-out under
     // bare `MinimalPlugins` test fixtures so existing tests that
     // don't init `Assets<Image>` keep working with the rest of the
-    // splash content unchanged).
+    // splash content unchanged). Also skipped when reduce-motion is
-    let scanline_handle = images.map(|mut images| images.add(build_scanline_image()));
+    // on — the scanline overlay is the "CRT scanline effect" the
+    // design-system spec calls out as non-essential motion under
+    // reduce-motion (`design-system.md` §Accessibility #3). Without
+    // it the boot screen still reads as terminal-themed; the
+    // scanlines are decorative.
+    let scanline_handle = if reduce_motion {
+        None
+    } else {
+        images.map(|mut images| images.add(build_scanline_image()))
+    };
 
     commands
         .spawn((
@@ -712,15 +727,29 @@ fn cursor_pulse_factor(age: Duration, period: f32, min: f32) -> f32 {
 ///
 /// No-op when no `SplashRoot` exists (the splash has already
 /// despawned, or we're under a test fixture that doesn't spawn one).
+///
+/// Under `Settings::reduce_motion_mode`, the per-frame pulse
+/// multiplier is skipped — the cursor still fades in / out with
+/// the global splash alpha (essential timing) but doesn't blink
+/// (decorative motion). Spec at `design-system.md` §Accessibility
+/// (#3): reduce-motion suppresses non-essential motion only;
+/// fade-in / fade-out timelines stay intact because the splash
+/// itself would otherwise hard-cut on/off, which is jarring.
 fn pulse_splash_cursor(
     roots: Query<&SplashAge, With<SplashRoot>>,
+    settings: Option<Res<SettingsResource>>,
     mut pulses: Query<(&SplashFadableBg, &mut BackgroundColor), With<SplashCursorPulse>>,
 ) {
     let Some(age) = roots.iter().next() else {
         return;
     };
     let global = splash_alpha(age.0).unwrap_or(0.0);
-    let pulse = cursor_pulse_factor(age.0, MOTION_PULSE_PERIOD_SECS, PULSE_ALPHA_MIN);
+    let reduce_motion = settings.is_some_and(|s| s.0.reduce_motion_mode);
+    let pulse = if reduce_motion {
+        1.0
+    } else {
+        cursor_pulse_factor(age.0, MOTION_PULSE_PERIOD_SECS, PULSE_ALPHA_MIN)
+    };
     let combined = (global * pulse).clamp(0.0, 1.0);
     for (fadable, mut bg) in &mut pulses {
         let mut c = fadable.base_color;
@@ -954,6 +983,46 @@ mod tests {
         );
     }
 
+    #[test]
+    fn splash_skips_scanline_overlay_under_reduce_motion() {
+        // The CRT scanline overlay is decorative motion that
+        // `Settings::reduce_motion_mode` suppresses per the
+        // design-system spec (§Accessibility #3). The splash
+        // root itself still spawns — the cursor still fades in
+        // and out (essential timing), but the scanline overlay
+        // node is omitted entirely.
+        use solitaire_data::Settings;
+        let mut app = App::new();
+        app.add_plugins(MinimalPlugins)
+            .add_plugins(bevy::asset::AssetPlugin::default())
+            .init_asset::<bevy::image::Image>()
+            .add_plugins(SplashPlugin);
+        app.init_resource::<ButtonInput<KeyCode>>();
+        app.init_resource::<ButtonInput<MouseButton>>();
+        app.insert_resource(SettingsResource(Settings {
+            first_run_complete: false,
+            reduce_motion_mode: true,
+            ..Settings::default()
+        }));
+        app.update();
+        // The splash root spawns (essential motion intact)
+        assert_eq!(
+            count_splash_roots(&mut app),
+            1,
+            "splash should still spawn under reduce-motion — only the scanline + pulse are gated",
+        );
+        // The scanline overlay is gone
+        let scanline_count = app
+            .world_mut()
+            .query::<&SplashScanlineOverlay>()
+            .iter(app.world())
+            .count();
+        assert_eq!(
+            scanline_count, 0,
+            "scanline overlay must NOT spawn under reduce-motion",
+        );
+    }
+
     #[test]
     fn splash_despawns_after_total_duration() {
         let mut app = headless_app();