feat(lang): L11 views and templates - the UI is markup, not code

A `view Name { field = x; function q(..); on e(..) }` declaration is the one bridge between a
program and its UI: it writes view_<name>() -> UiView, whose model is a Value of every field and
whose call runs a query or an event by name.

ludic.ui is a template runtime:
- HTML-shaped XML screens and components, loaded at run time;
- {expression} bindings, if/else/each, props, slots, per-instance state;
- on-press / onclick actions (event, set, emit);
- component libraries (export="true", <import src as>).

Styling:
- stylesheets in <style> or importable .lss files (@import);
- CSS selectors (#id, .class, [attr=v], descendant and > combinators, :hover, :disabled,
  :first-child, :last-child, :nth-child, :not) weighed by specificity;
- the box model and flex under CSS's property names.

Also:
- default parameters, and positional-then-named calls;
- Value gains a float kind;
- a function shadowing a runtime one is refused;
- an index is evaluated before the slice is read;
- runtime errors name the right file.

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

packages/ludic.ui/env.ludic

@@ -0,0 +1,65 @@
+# env.ludic - what a name means where an expression is read: the loop's own names, then the
+# component's props and state, then the view's model. A component sees its props, its state
+# and the model - never the names of whoever used it.
+export property UiEnv {
+  names: []string = null
+  vals: []Val = null
+  state: Val = null
+  parent: UiEnv = null
+  model: Val = null
+  slot: UiTpl = null
+  slot_env: UiEnv = null
+  on_names: []string = null      # a component's on-* attributes, which its `emit` runs
+  on_acts: []UiAct = null
+  on_envs: []UiEnv = null
+}
+var ui_view: UiView = null
+var ui_errs: []string = new []string
+
+function env_new(parent: UiEnv) -> UiEnv {
+  let e = new UiEnv
+  e.names = new []string
+  e.vals = new []Val
+  e.parent = parent
+  if parent != null { e.model = parent.model }
+  return e
+}
+function env_bind(e: UiEnv, name: string, v: Val) -> void {
+  push(e.names, name)
+  push(e.vals, v)
+}
+function env_get(e: UiEnv, name: string) -> Val {
+  var at = e
+  while at != null {
+    var i = len(at.names) - 1
+    while i >= 0 {
+      if at.names[i] == name { return at.vals[i] }
+      i -= 1
+    }
+    if at.state != null and Value.has(at.state, name) != 0 { return Value.get(at.state, name) }
+    at = at.parent
+  }
+  if e.model != null and Value.has(e.model, name) != 0 { return Value.get(e.model, name) }
+  ui_err(`no {name} here: not a loop's, a prop, a state or in the view`)
+  return Value.null()
+}
+# `set name = value`: the nearest state that holds the name
+function env_set(e: UiEnv, name: string, v: Val) -> void {
+  var at = e
+  while at != null {
+    if at.state != null and Value.has(at.state, name) != 0 {
+      Value.put(at.state, name, v)
+      return
+    }
+    at = at.parent
+  }
+  ui_err(`set {name}: no state here holds it - declare it with <state {name}="..."/>`)
+}
+# an error is said once, however many frames make it
+function ui_err(msg: string) -> void {
+  for i in 0 .. len(ui_errs) {
+    if ui_errs[i] == msg { return }
+  }
+  push(ui_errs, msg)
+  print(`ui: {msg}`)
+}