feat(lang): 0.S - a reference out of a read-only state is read-only (named so), a program's type named like the runtime's is refused (PadButton), tests for both, the migrate case covers lets; changeset

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

examples/rejected/module_let_alias.ludic

@@ -0,0 +1,9 @@
+# 0.S: a module-level let is immutable all the way down, through a local that holds it too
+program ModuleLetAlias {
+  let LIMITS: []int = [1, 2]
+  entry {
+    let l = LIMITS
+    push(l, 3)
+    print(len(LIMITS))
+  }
+}