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/dump.ludic

@@ -23,8 +23,8 @@ function dp_name(n: UiNode) -> string {
 function dp_style(n: UiNode) -> string {
   var s = ""
   if n.size > 0.0 { s = s + ` font {int(n.size)}` }
-  if n.fg >= 0 { s = s + ` color {n.fg}` }
-  if n.bg >= 0 { s = s + ` bg {n.bg}` }
+  if n.fg >= 0 { s = s + ` color {ui_hex(n.fg)}` }
+  if n.bg >= 0 { s = s + ` bg {ui_hex(n.bg)}` }
   if n.alpha < 1.0 { s = s + ` opacity {n.alpha}` }
   if n.pt + n.pr + n.pb + n.pl > 0.0 { s = s + ` pad {int(n.pt)} {int(n.pr)} {int(n.pb)} {int(n.pl)}` }
   if n.mt + n.mr + n.mb + n.ml > 0.0 { s = s + ` margin {int(n.mt)} {int(n.mr)} {int(n.mb)} {int(n.ml)}` }