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>

selfhost/frontend/parse.ludic

@@ -577,7 +577,9 @@ function parse_fn() -> Node {
   eat_op("(")
   if is_reserved_word(n.s) { perr(`'{n.s}' is a reserved word and cannot name a function`) }
   while not is_op(")") {
-    let p = node(N_PARAM); p.s = eat_id(); eat_op(":"); p.ty = ptype(); push(n.kids, p)
+    let p = node(N_PARAM); p.s = eat_id(); eat_op(":"); p.ty = ptype()
+    if is_op("=") { pi += 1;  p.a = expr() }       # L11: a default, for a call that leaves it out
+    push(n.kids, p)
     if is_op(",") { pi += 1 }
   }
   eat_op(")")
@@ -1014,6 +1016,7 @@ function parse_one_decl() -> void {
   if is_id("namespace") { parse_namespace(); return }   # #76 namespace block
   if is_id("registry") and (toks[pi + 1].kind == TK_ID) and (toks[pi + 2].text == "of") { parse_registry(); return }   # L8
   if is_id("def") and (toks[pi + 1].kind == TK_ID) and (toks[pi + 2].kind == TK_ID) { parse_def(); return }            # L8
+  if is_id("view") and (toks[pi + 1].kind == TK_ID) and (toks[pi + 2].text == "{") { parse_view(); return }            # L11
   if is_id("var")    { push(prog, parse_var()); return }
   if is_id("const")  { push(prog, parse_const()); return }
   var is_unsafe = false
@@ -1510,4 +1513,5 @@ function parse_program() -> void {
     parse_one_decl()
   }
   registries_finish()                              # L8: each registry gets its defs
+  views_finish()                                   # L11: each view gets its model and call
 }