feat(lang): a module's private names are its own

A private function, var or const no longer collides with the same
spelling in another module, in no module or in the runtime: where two
meet, each private one is renamed for its module (seed$shop), with every
reference its module writes that no local shadows. Exported names stay
one namespace. Nothing is renamed without a clash. Reseed.

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

examples/modules/twins/shop/index.ludic

@@ -0,0 +1,10 @@
+# shop/index.ludic - private names a neighbour also uses: seed, dice, LIMIT
+module shop
+var dice: int = 100
+const LIMIT: int = 5
+function seed() -> int {
+  return dice + LIMIT
+}
+export function shop_seed() -> int {
+  return seed()
+}