test(explore): add the factory-closure fixture and its selection probe (CG-27)

A file whose top-level symbol spans almost all of it — createFoo() returning
an object of closures — is how Svelte 5 rune stores, React custom-hook modules,
IIFE module-pattern JS and Zustand's create((set,get)=>({…})) are all written.
probe-factory-closure.mjs measures what such a file DELIVERS from within: which
inner symbols' definitions reach the agent, not how many bytes did.

__tests__/fixtures/factory-closure-ts/package.json

@@ -0,0 +1,5 @@
+{
+  "name": "factory-closure-ts",
+  "version": "0.0.0",
+  "private": true
+}