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/rejected/port_missing.ludic

@@ -0,0 +1,14 @@
+# L3: a bind gives every member that has no default
+program PortMissing {
+  port Clock {
+    now: fn() -> int
+    day: fn() -> int
+  }
+  function hours() -> int {
+    return 3
+  }
+  bind Clock { now: fn hours }
+  entry {
+    print(Clock.now())
+  }
+}