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.render3d/texture.ludic

@@ -274,8 +274,30 @@ function tex_load_ex(path: pointer, srgb: bool, dilate: int) -> int {
   if dilate > 0 { tex_dilate(px, 60, dilate) }
   let id = tex_upload(px, srgb, true)
   free(px)
+  tex_note_size(id)
   return id
 }
+# the size each loaded texture was, by id: a nine-slice or a UI image asks
+var tex_size_ids: []int = new []int
+var tex_size_ws: []int = new []int
+var tex_size_hs: []int = new []int
+function tex_note_size(id: int) -> void {
+  push(tex_size_ids, id)
+  push(tex_size_ws, tex_w)
+  push(tex_size_hs, tex_h)
+}
+function tex_width(id: int) -> int {
+  for i in 0 .. len(tex_size_ids) {
+    if tex_size_ids[i] == id { return tex_size_ws[i] }
+  }
+  return 0
+}
+function tex_height(id: int) -> int {
+  for i in 0 .. len(tex_size_ids) {
+    if tex_size_ids[i] == id { return tex_size_hs[i] }
+  }
+  return 0
+}
 
 # A small solid-colour fallback texture (linear rgb 0..255), for missing maps.
 function tex_solid(r: int, g: int, b: int, a: int) -> int {