feat(lang): UI components as files - component Name { ... } beside Name.xml and Name.lss

The compiler turns a component declaration into:
- a record of its props and state;
- a constructor, a props setter, a model and a call;
- a class, registered with ludic.ui at start.

Its template and styles are read from beside it and compiled in, with @import inlined, and a
missing template fails the build.

In the runtime:
- each mounted instance keeps its own props and state, and `set` in a template writes the state;
- styles are scoped to the component;
- class, style and id on a component's tag land on its root, styled by the parent's sheet too;
- ui_reload re-reads a component's files from disk and keeps instances.

The package's own module is now ludic_ui, so a program may call a directory of its own ui.

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

packages/ludic.ui/eval.ludic

@@ -42,8 +42,16 @@ function ev_call(x: UiExpr, e: UiEnv) -> Val {
     for i in 0 .. Value.as_int(Value.at(args, 0)) { Value.add(out, Value.int(i)) }
     return out
   }
+  var at = e
+  while at != null {
+    if at.inst != null {
+      let r = at.inst.cls.call(at.inst.ptr, x.s, args)
+      if Value.kind(r) != 99 { return r }
+    }
+    at = at.parent
+  }
   if ui_view == null or ui_view.call == null {
-    ui_err(`{x.s}(): no view is showing to ask`)
+    ui_err(`{x.s}(): there is no function or event of that name here`)
     return Value.null()
   }
   return ui_view.call(x.s, args)