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>

tests/unit/test_parent_child_system.py

@@ -0,0 +1,204 @@
+#!/usr/bin/env python3
+"""
+Test #122: Parent-Child UI System
+Test #102: Global Position Property
+Test #116: Dirty Flag System (partial - propagation)
+"""
+
+import mcrfpy
+import sys
+
+def test_parent_property():
+    """Test that children get parent reference when added to Frame"""
+    print("Testing parent property...")
+
+    # Create scene and get UI
+    mcrfpy.createScene("test")
+    ui = mcrfpy.sceneUI("test")
+
+    # Create a parent frame
+    parent = mcrfpy.Frame(pos=(100, 100), size=(200, 200))
+    ui.append(parent)
+
+    # Create a child caption
+    child = mcrfpy.Caption(text="Child", pos=(10, 10))
+
+    # Before adding, parent should be None
+    assert child.parent is None, f"Child should have no parent before adding, got: {child.parent}"
+
+    # Add child to parent
+    parent.children.append(child)
+
+    # After adding, parent should be set
+    assert child.parent is not None, "Child should have parent after adding"
+    # The parent should be the same Frame we added to
+    # (checking by position since identity comparison is tricky)
+    assert child.parent.x == parent.x, f"Parent x mismatch: {child.parent.x} vs {parent.x}"
+    assert child.parent.y == parent.y, f"Parent y mismatch: {child.parent.y} vs {parent.y}"
+
+    print("  - Parent property: PASS")
+
+
+def test_global_position():
+    """Test global position calculation through parent chain"""
+    print("Testing global_position property...")
+
+    # Create scene and get UI
+    mcrfpy.createScene("test2")
+    ui = mcrfpy.sceneUI("test2")
+
+    # Create nested hierarchy:
+    # root (50, 50)
+    #   -> child1 (20, 20) -> global (70, 70)
+    #       -> child2 (10, 10) -> global (80, 80)
+
+    root = mcrfpy.Frame(pos=(50, 50), size=(200, 200))
+    ui.append(root)
+
+    child1 = mcrfpy.Frame(pos=(20, 20), size=(100, 100))
+    root.children.append(child1)
+
+    child2 = mcrfpy.Caption(text="Deep", pos=(10, 10))
+    child1.children.append(child2)
+
+    # Check global positions
+    # root has no parent, global should equal local
+    assert root.global_position.x == 50, f"Root global x: expected 50, got {root.global_position.x}"
+    assert root.global_position.y == 50, f"Root global y: expected 50, got {root.global_position.y}"
+
+    # child1 is at (20, 20) inside root at (50, 50) -> global (70, 70)
+    assert child1.global_position.x == 70, f"Child1 global x: expected 70, got {child1.global_position.x}"
+    assert child1.global_position.y == 70, f"Child1 global y: expected 70, got {child1.global_position.y}"
+
+    # child2 is at (10, 10) inside child1 at global (70, 70) -> global (80, 80)
+    assert child2.global_position.x == 80, f"Child2 global x: expected 80, got {child2.global_position.x}"
+    assert child2.global_position.y == 80, f"Child2 global y: expected 80, got {child2.global_position.y}"
+
+    print("  - Global position: PASS")
+
+
+def test_parent_changes_on_move():
+    """Test that moving child to different parent updates parent reference"""
+    print("Testing parent changes on move...")
+
+    mcrfpy.createScene("test3")
+    ui = mcrfpy.sceneUI("test3")
+
+    parent1 = mcrfpy.Frame(pos=(0, 0), size=(100, 100), fill_color=(255, 0, 0, 255))
+    parent2 = mcrfpy.Frame(pos=(200, 0), size=(100, 100), fill_color=(0, 255, 0, 255))
+    ui.append(parent1)
+    ui.append(parent2)
+
+    child = mcrfpy.Caption(text="Movable", pos=(5, 5))
+    parent1.children.append(child)
+
+    # Child should be in parent1
+    assert child.parent is not None, "Child should have parent"
+    assert child.parent.x == 0, f"Child parent should be parent1, x={child.parent.x}"
+
+    # Move child to parent2 (should auto-remove from parent1)
+    parent2.children.append(child)
+
+    # Child should now be in parent2
+    assert child.parent is not None, "Child should still have parent"
+    assert child.parent.x == 200, f"Child parent should be parent2, x={child.parent.x}"
+
+    # parent1 should have no children
+    assert len(parent1.children) == 0, f"parent1 should have 0 children, has {len(parent1.children)}"
+
+    # parent2 should have one child
+    assert len(parent2.children) == 1, f"parent2 should have 1 child, has {len(parent2.children)}"
+
+    print("  - Parent changes on move: PASS")
+
+
+def test_remove_clears_parent():
+    """Test that removing child clears parent reference"""
+    print("Testing remove clears parent...")
+
+    mcrfpy.createScene("test4")
+    ui = mcrfpy.sceneUI("test4")
+
+    parent = mcrfpy.Frame(pos=(0, 0), size=(100, 100))
+    ui.append(parent)
+
+    child = mcrfpy.Caption(text="Removable", pos=(5, 5))
+    parent.children.append(child)
+
+    assert child.parent is not None, "Child should have parent"
+
+    # Remove child
+    parent.children.remove(child)
+
+    assert child.parent is None, f"Child should have no parent after remove, got: {child.parent}"
+    assert len(parent.children) == 0, f"Parent should have no children after remove"
+
+    print("  - Remove clears parent: PASS")
+
+
+def test_scene_level_elements():
+    """Test that scene-level elements have no parent"""
+    print("Testing scene-level elements...")
+
+    mcrfpy.createScene("test5")
+    ui = mcrfpy.sceneUI("test5")
+
+    frame = mcrfpy.Frame(pos=(10, 10), size=(50, 50))
+    ui.append(frame)
+
+    # Scene-level elements should have no parent
+    assert frame.parent is None, f"Scene-level element should have no parent, got: {frame.parent}"
+
+    # Global position should equal local position
+    assert frame.global_position.x == 10, f"Global x should equal local x"
+    assert frame.global_position.y == 10, f"Global y should equal local y"
+
+    print("  - Scene-level elements: PASS")
+
+
+def test_all_drawable_types():
+    """Test parent/global_position on all drawable types"""
+    print("Testing all drawable types...")
+
+    mcrfpy.createScene("test6")
+    ui = mcrfpy.sceneUI("test6")
+
+    parent = mcrfpy.Frame(pos=(100, 100), size=(300, 300))
+    ui.append(parent)
+
+    # Test all types
+    types_to_test = [
+        ("Frame", mcrfpy.Frame(pos=(10, 10), size=(50, 50))),
+        ("Caption", mcrfpy.Caption(text="Test", pos=(10, 70))),
+        ("Sprite", mcrfpy.Sprite(pos=(10, 130))),  # May need texture
+        ("Grid", mcrfpy.Grid(grid_size=(5, 5), pos=(10, 190), size=(80, 80))),
+    ]
+
+    for name, child in types_to_test:
+        parent.children.append(child)
+        assert child.parent is not None, f"{name} should have parent"
+        # Global position should be local + parent's position
+        expected_x = child.x + 100
+        expected_y = child.y + 100
+        assert child.global_position.x == expected_x, f"{name} global_x: expected {expected_x}, got {child.global_position.x}"
+        assert child.global_position.y == expected_y, f"{name} global_y: expected {expected_y}, got {child.global_position.y}"
+
+    print("  - All drawable types: PASS")
+
+
+if __name__ == "__main__":
+    try:
+        test_parent_property()
+        test_global_position()
+        test_parent_changes_on_move()
+        test_remove_clears_parent()
+        test_scene_level_elements()
+        test_all_drawable_types()
+
+        print("\n=== All tests passed! ===")
+        sys.exit(0)
+    except Exception as e:
+        print(f"\nTEST FAILED: {e}")
+        import traceback
+        traceback.print_exc()
+        sys.exit(1)