[AIAA] Add Copilot cloud agent environment setup workflow

.github/workflows/copilot-setup-steps.yml

@@ -0,0 +1,26 @@
+# Prepares the Copilot cloud agent's ephemeral environment before the
+# model starts: Node from .nvmrc, npm cache, npm ci. Runs on changes to
+# itself so pull requests validate it; takes effect for agent sessions
+# once merged to the default branch.
+
+name: Copilot Setup Steps
+
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+jobs:
+  # The job must be called copilot-setup-steps or the agent ignores it.
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@v6
+      - uses: ./.github/actions/npm-ci-via-cached-nvmrc