fix(engine): resolve all clippy warnings introduced by PNG asset pipeline

- Collapse nested-if patterns into let-chains across 13 plugins (42 instances)
- Add #[allow(clippy::too_many_arguments)] to 5 Bevy systems in card_plugin
  and input_plugin where ECS parameter count exceeds the lint threshold
- Gate Theme import in table_plugin under #[cfg(test)] — only used by
  test-only colour helpers; removing the unconditional import silences the
  unused-import lint without breaking the test suite
- Wrap ButtonInput<MouseButton> in Option<> in update_input_platform so that
  tests using MinimalPlugins (no InputPlugin) no longer panic on startup

All 789 tests pass; cargo clippy --workspace -- -D warnings is clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_engine/src/card_animation/tuning.rs

@@ -148,7 +148,7 @@ impl Default for AnimationTuning {
 /// running under `MinimalPlugins` (which does not register the touch subsystem).
 pub(crate) fn update_input_platform(
     touches: Option<Res<Touches>>,
-    mouse_buttons: Res<ButtonInput<MouseButton>>,
+    mouse_buttons: Option<Res<ButtonInput<MouseButton>>>,
     mut tuning: ResMut<AnimationTuning>,
 ) {
     let touch_active = touches.as_ref().is_some_and(|t| {
@@ -157,8 +157,9 @@ pub(crate) fn update_input_platform(
             || t.iter_just_released().next().is_some()
     });
 
-    let mouse_active = mouse_buttons.get_just_pressed().next().is_some()
-        || mouse_buttons.get_pressed().next().is_some();
+    let mouse_active = mouse_buttons.as_ref().is_some_and(|mb| {
+        mb.get_just_pressed().next().is_some() || mb.get_pressed().next().is_some()
+    });
 
     if touch_active && tuning.platform != InputPlatform::Touch {
         *tuning = AnimationTuning::mobile();