feat(lang): ports - port Clock { ... } in a module, bind Clock { ... } in the app

A port is a record of function values a module calls through
(Clock.now()) without naming the module that answers. A port used and
never bound, a bind missing a required member or naming one the port
lacks, and a second bind are refused; the binder must see the port, and
what it binds is checked from its own file. Reseed.

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

examples/modules/station/app/index.ludic

@@ -0,0 +1,10 @@
+# app/index.ludic - the app puts the program together: it sees the port and fills it
+module app uses clock
+bind Clock { now: fn game_hours }
+var g_hours: int = 30
+function game_hours() -> int {
+  return g_hours
+}
+export function advance(h: int) -> void {
+  g_hours += h
+}