adding the first run wizard again

src/lib/encounter-budget.test.ts

@@ -0,0 +1,6 @@
+// ponytail: reuses the in-source demo() self-check so there's one set of
+// assertions, not two. Run: node scripts/check-encounter-budget.ts (or any
+// TS runner). No test framework, no @types/node dependency.
+import { demo } from "./encounter-budget";
+
+demo();