feat(ui): ludic.ui grows toward HTML, CSS and React (Phase 0.U1-U4)

- Natives: ui_native(tag, measure, draw) makes an element the program draws itself; ui_fire
  runs its on-<event> with event.value. input, select and textarea have simple defaults.
- React:
  - keyed <each>, <let>, <provide> context through components, <fragment>;
  - named slots, default props on <component>;
  - on-mount / on-unmount;
  - inline text inside text elements.
- CSS:
  - custom properties and var();
  - position relative/absolute/fixed with insets and z-index;
  - em/rem/vw/vh and @media;
  - wrapping text and ellipsis, overflow;
  - + and ~ combinators, :nth-child(an+b), :checked, :active.
- Developing: errors with file:line, ui_errors(), ui_reload() keeping state, and an
  inspector-style ui_dump.
- view fields infer the type of a literal or a named function's result.

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

packages/ludic.ui/frame.ludic

@@ -1,17 +1,18 @@
 # frame.ludic - a screen shown: built from the view's model, laid out, drawn, and its presses
 # run once the frame is drawn, so nothing the view does can change a frame half way through it
 var fr_was_down: bool = false
-var fr_pressed: []UiNode = new []UiNode
+var fr_down_now: bool = false
 
 export function ui_show(screen: string, view: UiView, x: float, y: float, w: float, h: float) -> void {
+  ui_viewport(w, h)
   let root = ui_nodes(screen, view)
   if root == null { return }
   ui_place(root, x, y, w, h)
-  fr_pressed = new []UiNode
+  nt_fired_clear()
   fr_pointer(root)
   if ui_be != null and ui_be.text != null { fr_draw(root) }
-  let pressed = fr_pressed
-  for i in 0 .. len(pressed) { ui_press(pressed[i]) }
+  lc_run(screen)
+  nt_fired_run()
 }
 # the screen's nodes for this frame, not yet laid out - for a test, or a host that places them
 export function ui_nodes(screen: string, view: UiView) -> UiNode {
@@ -21,6 +22,7 @@ export function ui_nodes(screen: string, view: UiView) -> UiNode {
     return null
   }
   let t = lib_screens[si]
+  lc_begin()
   ui_view = view
   let e = env_new(null)
   if view != null and view.model != null { e.model = view.model() } else { e.model = Value.object() }
@@ -34,15 +36,22 @@ export function ui_nodes(screen: string, view: UiView) -> UiNode {
   root.akeys = new []string
   root.avals = new []string
   root.vals = new []Val
+  root.tag = "screen"
   for i in 0 .. len(t.keys) {
     if t.keys[i] != "name" { el_keep(root, t.keys[i], ui_eval(t.vals[i], e)) }
   }
-  for i in 0 .. len(root.akeys) { el_apply(root, root.akeys[i], root.vals[i]) }
   bd_kids(t.kids, e, screen, root.children)
   cs_tree(root)
   return root
 }
+# the room vw, vh and @media measure against; ui_show sets it to the screen's rectangle
+export function ui_viewport(w: float, h: float) -> void {
+  ly_vp_w = w
+  ly_vp_h = h
+}
 export function ui_place(root: UiNode, x: float, y: float, w: float, h: float) -> void {
+  ly_vp_x = x
+  ly_vp_y = y
   root.w = UI_FILL
   root.h = UI_FILL
   var fg = 15658734
@@ -54,6 +63,8 @@ export function ui_place(root: UiNode, x: float, y: float, w: float, h: float) -
 export function ui_press(n: UiNode) -> void {
   if n.act != null and n.enabled { act_run(n.act, n.env) }
 }
+# any event, as if the element had fired it - for a test
+export function ui_event(n: UiNode, name: string, value: Val) -> void { nt_run(n, name, value) }
 # the pointer: what it is over is :hover next frame (the element and all around it, as in CSS),
 # and without a renderer's own button a press on the deepest pressable thing is a press
 var fr_hover: []string = new []string
@@ -68,10 +79,14 @@ function fr_pointer(root: UiNode) -> void {
   let keys = new []string
   fr_under(root, px, py, keys)
   fr_hover = keys
-  if ui_be.button != null or ui_be.pointer_down == null { return }
-  let hit = fr_hit(root, px, py)
+  if ui_be.pointer_down == null { return }
   let down = ui_be.pointer_down()
-  if hit != null and down and not fr_was_down { push(fr_pressed, hit) }
+  fr_down_now = down
+  if ui_be.button != null { return }
+  let hit = fr_hit(root, px, py)
+  if hit != null and down and not fr_was_down and hit.enabled {
+    if hit.kind == UI_NATIVE { fm_press(hit) } else { ui_fire(hit, "press", Value.null()) }
+  }
   fr_was_down = down
 }
 function fr_under(n: UiNode, px: float, py: float, keys: []string) -> void {
@@ -89,7 +104,7 @@ function fr_hit(n: UiNode, px: float, py: float) -> UiNode {
       i -= 1
     }
   }
-  if n.act != null { return n }
+  if n.act != null or (n.kind == UI_NATIVE and n.on_names != null and len(n.on_names) > 0) { return n }
   return null
 }
 export function ui_hit(root: UiNode, px: float, py: float) -> UiNode { return fr_hit(root, px, py) }