feat: add apex launcher, test runner, and cli smoke test

apex

@@ -0,0 +1,17 @@
+#!/usr/bin/env python3
+"""apex launcher — stdlib only. Puts commons/ (+ vendor/ + proprietaries/) on sys.path."""
+import os
+import sys
+
+_here = os.path.dirname(os.path.realpath(__file__))     # commons dir (or standalone repo root)
+sys.path.insert(0, _here)                               # make `engine` importable
+_vendor = os.path.join(_here, "vendor")
+if os.path.isdir(_vendor):
+    sys.path.insert(0, _vendor)
+if os.path.basename(_here) == "commons":                # node checkout: expose proprietaries/lib
+    _prop = os.path.join(os.path.dirname(_here), "proprietaries")
+    if os.path.isdir(_prop):
+        sys.path.insert(0, _prop)
+
+from engine.cli import main  # noqa: E402
+raise SystemExit(main(sys.argv[1:]))