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/UIBase.h

@@ -162,4 +162,18 @@ static int UIDrawable_set_opacity(T* self, PyObject* value, void* closure)
          "Automatically clamped to valid range [0.0, 1.0]." \
      ), NULL}
 
+// #122 & #102: Macro for parent/global_position properties (requires closure with type enum)
+// These need the PyObjectsEnum value in closure, so they're added separately in each class
+#define UIDRAWABLE_PARENT_GETSETTERS(type_enum) \
+    {"parent", (getter)UIDrawable::get_parent, NULL, \
+     MCRF_PROPERTY(parent, \
+         "Parent drawable (read-only). " \
+         "Returns the parent Frame/Grid if nested, or None if at scene level." \
+     ), (void*)type_enum}, \
+    {"global_position", (getter)UIDrawable::get_global_pos, NULL, \
+     MCRF_PROPERTY(global_position, \
+         "Global screen position (read-only). " \
+         "Calculates absolute position by walking up the parent chain." \
+     ), (void*)type_enum}
+
 // UIEntity specializations are defined in UIEntity.cpp after UIEntity class is complete