Add JS toolchain: TypeScript, ESLint, Prettier, Vitest

package.json declares the project as ESM with NodeNext module resolution,
exposing dist/index.js as the library entry and dist/bin/quack.js as the
CLI binary. Dev dependencies are pinned to exact versions (yarn.lock holds
the integrity hashes per repo policy on hash-pinned external references).
Adds a placeholder src/index.ts and a single smoke test so make check is
not a no-op.

test/smoke.test.ts

@@ -0,0 +1,9 @@
+import { describe, expect, it } from "vitest";
+import { VERSION } from "../src/index.js";
+
+describe("quack", () => {
+    it("exports a version string", () => {
+        expect(typeof VERSION).toBe("string");
+        expect(VERSION.length).toBeGreaterThan(0);
+    });
+});