feat: Implement Phase A UI hierarchy foundations (closes #122, #102, #116, #118)

Parent-Child UI System (#122):
- Add parent weak_ptr to UIDrawable for hierarchy tracking
- Add setParent(), getParent(), removeFromParent() methods
- UICollection now tracks owner and sets parent on append/insert
- Auto-remove from old parent when adding to new collection

Global Position Property (#102):
- Add get_global_position() that walks up parent chain
- Expose as read-only 'global_position' property on all UI types
- Add UIDRAWABLE_PARENT_GETSETTERS macro for consistent bindings

Dirty Flag System (#116):
- Modify markDirty() to propagate up the parent chain
- Add isDirty() and clearDirty() methods for render optimization

Scene as Drawable (#118):
- Add position, visible, opacity properties to Scene
- Add setProperty()/getProperty() for animation support
- Apply scene transformations in PyScene::render()
- Fix lifecycle callbacks to clear errors when methods don't exist
- Add GameEngine::getScene() public accessor

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/Scene.h

@@ -35,12 +35,22 @@ public:
     bool hasAction(std::string);
     bool hasAction(int);
     std::string action(int);
-    
-    
+
+
     std::shared_ptr<std::vector<std::shared_ptr<UIDrawable>>> ui_elements;
 
     //PyObject* key_callable;
     std::unique_ptr<PyKeyCallable> key_callable;
     void key_register(PyObject*);
     void key_unregister();
+
+    // #118: Scene-level UIDrawable-like properties for animations/transitions
+    sf::Vector2f position{0.0f, 0.0f};  // Offset applied to all ui_elements
+    bool visible = true;                 // Controls rendering of scene
+    float opacity = 1.0f;                // Applied to all ui_elements (0.0-1.0)
+
+    // Animation support for scene properties
+    bool setProperty(const std::string& name, float value);
+    bool setProperty(const std::string& name, const sf::Vector2f& value);
+    float getProperty(const std::string& name) const;
 };