feat(FN-4093): refactor PR checks workflow with new setup-node-pnpm composi

FN-4093 introduced a reusable `setup-node-pnpm` composite GitHub Action and refactored the PR checks workflow to use it, reducing the workflow file by over 60 lines while adding a contract test for the action. A small follow-up stabilizes workspace quality gates by adding an export in the core store

Fusion-Task-Id: FN-4093

packages/cli/src/__tests__/ci-workflow.test.ts

@@ -183,9 +183,7 @@ describe("PR checks workflow (.github/workflows/pr-checks.yml)", () => {
     expect(
       lintSteps.some(
         (step: any) =>
-          step.name === "Install dependencies" &&
-          typeof step.run === "string" &&
-          step.run.includes("pnpm install --frozen-lockfile"),
+          typeof step.uses === "string" && step.uses.includes("./.github/actions/setup-node-pnpm"),
       ),
     ).toBe(true);
     expect(