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/weather/index.ludic

@@ -0,0 +1,13 @@
+# weather/index.ludic - the same private spellings, its own; a local named dice is its own too
+module weather
+var dice: int = 20
+const LIMIT: int = 2
+function seed() -> int {
+  return dice * LIMIT
+}
+function roll(dice: int) -> int {
+  return dice + 1
+}
+export function weather_seed() -> int {
+  return seed() + roll(0)
+}