test(metatype): self-reference regression example (recursive *List enum)

examples/0618 mints a recursive `List` enum (`cons: *List; nil`) via
declare("List")/define, builds a 3-node list, matches the pointer payload
directly and via deref, and counts it recursively. Locks the self-reference
capability. Full suite green (674).

examples/expected/0618-comptime-metatype-self-reference.exit

@@ -0,0 +1 @@
+0

examples/expected/0618-comptime-metatype-self-reference.stderr

@@ -0,0 +1 @@
+

examples/expected/0618-comptime-metatype-self-reference.stdout

@@ -0,0 +1,2 @@
+c -> cons
+len = 2