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

.github/workflows/pr-checks.yml

@@ -14,20 +14,8 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Install pnpm
-        uses: pnpm/action-setup@v4
-
-      - name: Setup Node.js
-        uses: actions/setup-node@v5
-        with:
-          node-version: "24"
-          cache: pnpm
-
-      - name: Install dependencies
-        run: pnpm install --frozen-lockfile
+      - name: Setup Node.js and pnpm
+        uses: ./.github/actions/setup-node-pnpm
 
       - name: Lint
         run: pnpm lint
@@ -37,20 +25,8 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Install pnpm
-        uses: pnpm/action-setup@v4
-
-      - name: Setup Node.js
-        uses: actions/setup-node@v5
-        with:
-          node-version: "24"
-          cache: pnpm
-
-      - name: Install dependencies
-        run: pnpm install --frozen-lockfile
+      - name: Setup Node.js and pnpm
+        uses: ./.github/actions/setup-node-pnpm
 
       - name: Typecheck
         run: pnpm typecheck
@@ -60,20 +36,8 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Install pnpm
-        uses: pnpm/action-setup@v4
-
-      - name: Setup Node.js
-        uses: actions/setup-node@v5
-        with:
-          node-version: "24"
-          cache: pnpm
-
-      - name: Install dependencies
-        run: pnpm install --frozen-lockfile
+      - name: Setup Node.js and pnpm
+        uses: ./.github/actions/setup-node-pnpm
 
       - name: Install Bun
         uses: oven-sh/setup-bun@v2
@@ -90,20 +54,8 @@ jobs:
         shard: [1, 2, 3]
 
     steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Install pnpm
-        uses: pnpm/action-setup@v4
-
-      - name: Setup Node.js
-        uses: actions/setup-node@v5
-        with:
-          node-version: "24"
-          cache: pnpm
-
-      - name: Install dependencies
-        run: pnpm install --frozen-lockfile
+      - name: Setup Node.js and pnpm
+        uses: ./.github/actions/setup-node-pnpm
 
       - name: Install Bun
         uses: oven-sh/setup-bun@v2