feat(ui): linear-gradient backgrounds, object-fit and aspect-ratio

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.ui/render3d.ludic

@@ -31,6 +31,8 @@ export function ui_render3d() -> void {
   b.text = fn r3u_text
   b.measure = fn r3u_measure
   b.image = fn r3u_image
+  b.image_w = fn r3u_image_w
+  b.image_h = fn r3u_image_h
   b.nine = fn r3u_nine
   b.clip = fn r3u_clip
   b.unclip = fn r3u_unclip