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/state.ludic

@@ -0,0 +1,34 @@
+# state.ludic - a component's or a screen's own values, <state name="{first}"/>, kept from frame
+# to frame by where the instance is in the tree, and set by `set name = value`
+var st_keys: []string = new []string
+var st_vals: []Val = new []Val
+function st_for(key: string, t: UiTpl, e: UiEnv) -> Val {
+  var decl: UiTpl = null
+  for i in 0 .. len(t.kids) {
+    if t.kids[i].tag == "state" { decl = t.kids[i] }
+  }
+  if decl == null { return null }
+  for i in 0 .. len(st_keys) {
+    if st_keys[i] == key { return st_vals[i] }
+  }
+  let o = Value.object()
+  for i in 0 .. len(decl.keys) { Value.put(o, decl.keys[i], ui_eval(decl.vals[i], e)) }
+  push(st_keys, key)
+  push(st_vals, o)
+  return o
+}
+# a screen's state starts again the next time it opens
+export function ui_forget(screen: string) -> void {
+  let keys = new []string
+  let vals = new []Val
+  for i in 0 .. len(st_keys) {
+    let k = st_keys[i]
+    let mine = len(k) >= len(screen) and k[0..len(screen)] == screen and (len(k) == len(screen) or k[len(screen)] == 47)
+    if not mine {
+      push(keys, k)
+      push(vals, st_vals[i])
+    }
+  }
+  st_keys = keys
+  st_vals = vals
+}