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/tpl_lines.ludic

@@ -17,3 +17,28 @@ function tp_line(at: int) -> int {
   return lo + 1
 }
 
+# text beside elements (<button><img/>Resume</button>): each run of it a text of its own, in order
+function tp_mixed(x: Xml) -> bool {
+  if Xml.child_count(x) == 0 or x.tag == "style" { return false }
+  for i in 0 .. len(x.mixed) {
+    if x.mixed[i].tag == "#text" { return true }
+  }
+  return false
+}
+function tp_read_mixed(t: UiTpl, x: Xml, file: string, err: []string) -> void {
+  for i in 0 .. len(x.mixed) {
+    let m = x.mixed[i]
+    if m.tag == "#text" {
+      let r = new UiTpl
+      r.tag = "#text"
+      r.where = t.where
+      r.keys = new []string
+      r.vals = new []UiExpr
+      r.on_keys = new []string
+      r.on_acts = new []UiAct
+      r.kids = new []UiTpl
+      r.text = ex_text(tpl_words(m.text), err)
+      push(t.kids, r)
+    } else { push(t.kids, tpl_read(m, file)) }
+  }
+}