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/hud_plugin.rs

@@ -437,15 +437,14 @@ fn update_hud(
     // Reflects the AutoCompleteState resource; update whenever it changes or game changes.
     let ac_active = auto_complete.as_ref().is_some_and(|ac| ac.active);
     let ac_changed = auto_complete.as_ref().is_some_and(|ac| ac.is_changed());
-    if ac_changed || game.is_changed() {
-        if let Ok(mut t) = auto_q.single_mut() {
+    if (ac_changed || game.is_changed())
+        && let Ok(mut t) = auto_q.single_mut() {
             **t = if ac_active {
                 "AUTO".to_string()
             } else {
                 String::new()
             };
         }
-    }
 }
 
 /// Updates the `HudSelection` text node to show which pile is Tab-selected.