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/node.ludic

@@ -6,6 +6,8 @@ export const UI_BUTTON: int = 3
 export const UI_SCROLL: int = 4
 export const UI_IMAGE: int = 5
 export const UI_RULE: int = 6         # <hr>: a line across
+export const UI_NATIVE: int = 7       # an element the host draws itself (ui_native)
+export const UI_AUTO: float = -1000000.0   # an inset that is not set
 export const UI_COL: int = 0
 export const UI_ROW: int = 1
 export const UI_FILL: float = -1.0
@@ -69,15 +71,30 @@ export property UiNode {
   min_h: float = 0.0
   max_h: float = 0.0
   hidden: bool = false          # display: none, or hidden
+  pos: int = 0                  # position: 0 static, 1 relative, 2 absolute, 3 fixed
+  top: float = -1000000.0       # the insets a positioned element is placed by (UI_AUTO: unset)
+  right: float = -1000000.0
+  bottom: float = -1000000.0
+  left: float = -1000000.0
+  z: int = 0
+  nowrap: bool = false          # white-space: nowrap
+  ellipsis: bool = false        # text-overflow: ellipsis
+  lines: []string = null        # a wrapped text's lines
+  var_names: []string = null    # its custom properties (--name), which its descendants inherit
+  var_vals: []string = null
   fg: int = -1
   bg: int = -2
   alpha: float = 1.0
   enabled: bool = true
-  act: UiAct = null
+  act: UiAct = null             # on-press, which the pointer and the renderer's button fire
+  on_names: []string = null     # every on-* it answers
+  on_acts: []UiAct = null
+  native: UiNative = null
   env: UiEnv = null
   children: []UiNode = null
   mw: float = 0.0
   mh: float = 0.0
+  content_h: float = 0.0         # what a scroll box holds, however tall the box itself is
   x: float = 0.0
   y: float = 0.0
   cw: float = 0.0