refactor(bloques2-5): auditoria de codi - limpieza i arquitectura

Bloque 2: eliminar codi mort comentat (shape_manager, engine)
Bloque 3: Engine shape methods com thin wrappers a ShapeManager;
          eliminar estat duplicat de shapes en Engine
Bloque 4: encapsular getBallsMutable() amb helpers a SceneManager
          (enableShapeAttractionAll, resetDepthScalesAll)
Bloque 5: StateManager Phase 9 - tota la logica DEMO/LOGO
          implementada directament amb refs a SceneManager,
          ThemeManager i ShapeManager; eliminar callbacks a Engine.
          Acoplament Engine<->StateManager passa a unidireccional.

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

source/scene/scene_manager.cpp

@@ -239,3 +239,15 @@ void SceneManager::updateBallSizes(int old_size, int new_size) {
         ball->updateSize(new_size);
     }
 }
+
+void SceneManager::enableShapeAttractionAll(bool enabled) {
+    for (auto& ball : balls_) {
+        ball->enableShapeAttraction(enabled);
+    }
+}
+
+void SceneManager::resetDepthScalesAll() {
+    for (auto& ball : balls_) {
+        ball->setDepthScale(1.0f);
+    }
+}