feat(ui): ludic.ui is a UI framework - input, controls, render3d backend, the CSS a game needs

A game no longer writes a host:
- The runtime reads Input itself: focus and keyboard navigation (Tab, arrows, Enter/Space,
  autofocus), the pointer (hover, :active, click on release, drag), and scroll boxes with the
  wheel, a draggable scrollbar, clipping and scroll-into-view.
- HTML's controls are built in (button, checkbox, radio, range, select, text, key capture), made
  of plain parts a stylesheet styles, each reporting with on-change and event.value.
- ludic.ui/render3d.ludic draws with render3d's overlay: textures, named atlases (icon:NAME),
  nine-slice border-image, rounded rects and rings, clipping, and a scale.
- Hooks for the program's language, sounds and clock (ui_translator, ui_sounds, ui_clock).
- ui_dev: hot reload, errors on screen, LUDIC_UI_DUMP.
- CSS:
  - colours as #rgb / #rrggbbaa / rgb() / rgba() / names;
  - border-radius and outline (following the radius), box-shadow, background-image and a tinted
    border-image;
  - group opacity, @keyframes / animation, transition;
  - :focus, :focus-visible and :focus-within.
- HTML mixed content, and boolean attributes.
- render3d gains tex_width / tex_height, and the XML reader keeps text runs in order.

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

packages/ludic.ui/cascade.ludic

@@ -22,6 +22,8 @@ function cs_node(n: UiNode) -> void {
   if n.style != null { cs_rule(n, n.style) }
   if n.style2 != null { cs_rule_in(n, n.style2, n.env2) }
   for i in 0 .. len(n.akeys) { el_apply(n, n.akeys[i], n.vals[i]) }
+  an_apply(n)
+  tr_apply(n)
 }
 function cs_sheet(n: UiNode, sh: UiSheet) -> void {
   for i in 0 .. len(sh.rules) {
@@ -39,8 +41,6 @@ function cs_rule_in(n: UiNode, r: UiRule, e: UiEnv) -> void {
     if not (len(r.keys[j]) > 2 and r.keys[j][0..2] == "--") { el_attr(n, r.keys[j], ui_eval(r.vals[j], e)) }
   }
 }
-# what every element looks like before anyone styles it, as a browser's own sheet does
-const UA_LSS: string = "h1 { font-size: 32 } h2 { font-size: 26 } h3 { font-size: 22 } h4 { font-size: 19 } h5 { font-size: 16 } h6 { font-size: 14 } small { font-size: 13 } button { padding: 5 10 } hr { height: 1; width: fill; background: #808080; margin: 4 0 } scroll { width: fill; height: fill } img { width: 24; height: 24 }"
 var ua_sh: UiSheet = null
 function ua_sheet() -> UiSheet {
   if ua_sh != null { return ua_sh }