feat(FN-2614): merge fusion/fn-2614 (auto-resolved)

- feat(FN-2614): complete Step 4 — configure vitest test isolation setup
- test(FN-2614): complete Step 3 — add isolation companion test
- feat(FN-2614): complete Step 2 — add test home isolation setup

packages/pi-claude-cli/src/__tests__/setup-test-isolation.ts

@@ -0,0 +1,6 @@
+import { mkdtempSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+const tempHome = mkdtempSync(join(tmpdir(), "fn-test-home-"));
+process.env.HOME = tempHome;