fix(lang): 0.R4 - ludic.ui's UiAct is its own, and a name that meets a package's export says whose it is

A game's exported UiAct collided with ludic.ui's, which nothing outside ludic.ui uses: it is private
to ludic.ui now, and a private record of one spelling in two modules never clashed. A real clash - a
type named like one a package exports - is still refused, and the message names the package and the
way out (`ludic_ui exports it, and exported names are one namespace - rename this one, or declare it
without export inside a module of your own`).

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

examples/rejected/pkg_export_clash.ludic

@@ -0,0 +1,7 @@
+# a program's type named like a package's export is a real clash, and the message says whose
+import "ludic.ui"
+program PkgClash {
+  numbers float
+  property UiNode { kind: int = 3 }
+  entry { print("x") }
+}