Grid now supports a `children` collection for arbitrary UIDrawable elements
(speech bubbles, effects, highlights, path visualization, etc.) that
automatically transform with the grid's camera (pan/zoom).
Key features:
- Children positioned in grid-world pixel coordinates
- Render after entities, before FOV overlay (proper z-ordering)
- Sorted by z_index, culled when outside visible region
- Click detection transforms through grid camera
- Automatically clipped to grid boundaries via RenderTexture
Python API:
grid.children.append(caption) # Speech bubble follows grid camera
grid.children.append(circle) # Highlight indicator
Closes#132🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
