ci: bump checkout/setup-node/upload+download-artifact v4 → v5

The v4 actions target Node.js 20, which GitHub now force-runs on Node 24
and flags as deprecated. Bump all four across every workflow to v5 (their
native Node-24 line) to clear the warning. Mechanical version-only change;
upload/download-artifact stay on matching majors as required.

Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_01DwbE3uTiFaKRNjx5vP2muV

.github/workflows/agent-pr-review.yml

@@ -17,14 +17,14 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
         with:
           ref: ${{ github.event.pull_request.head.ref }}
           repository: ${{ github.event.pull_request.head.repo.full_name }}
           fetch-depth: 0
 
       - name: Set up Node.js
-        uses: actions/setup-node@v4
+        uses: actions/setup-node@v5
         with:
           node-version: 22
           cache: 'npm'