chore: scaffold tracks and tooling

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

fixtures/m00-sanity.json

@@ -0,0 +1,7 @@
+{
+  "function": "sanity",
+  "cases": [
+    { "name": "one-plus-one", "args": [1, 1], "expected": 2 },
+    { "name": "two-plus-three", "args": [2, 3], "expected": 5 }
+  ]
+}