feat(workflow): add copilot-setup-steps.yml for Coding Agent environment

Create copilot-setup-steps.yml workflow to pre-install tools for GitHub
Copilot Coding Agent, bridging the devcontainer environment to GitHub
Actions runners.

Workflow includes:
- SHA-pinned actions (checkout, setup-node, setup-python)
- Node.js 20 with npm ci for JavaScript dependencies
- Python 3.11
- PowerShell modules (PowerShell-Yaml)

Update copilot-instructions.md with Coding Agent Environment section
documenting pre-installed tools and npm script usage.

Author: katriendg

.github/copilot-instructions.md

@@ -93,3 +93,31 @@ All tracking files use markdown format with frontmatter and follow patterns from
 
 PowerShell scripts follow PSScriptAnalyzer rules from `PSScriptAnalyzer.psd1` and include proper comment-based help. Validation runs via `npm run psscriptanalyzer` with results output to `logs/`.
 <!-- </script-operations> -->
+
+<!-- <coding-agent-environment> -->
+## Coding Agent Environment
+
+Copilot Coding Agent uses a cloud-based GitHub Actions environment, separate from the local devcontainer. The `.github/workflows/copilot-setup-steps.yml` workflow pre-installs tools to match devcontainer capabilities.
+
+### Pre-installed Tools
+
+* Node.js 20 with npm dependencies from `package.json`
+* Python 3.11
+* PowerShell 7 with Pester 5.7.1 and PowerShell-Yaml modules
+* shellcheck for bash script validation (pre-installed on ubuntu-latest)
+
+### Using npm Scripts
+
+Agents should use npm scripts for all validation:
+
+* `npm run lint:md` - Markdown linting
+* `npm run lint:ps` - PowerShell analysis
+* `npm run lint:yaml` - YAML validation
+* `npm run lint:frontmatter` - Frontmatter validation
+* `npm run lint:all` - Run all linters
+* `npm run test:ps` - PowerShell tests
+
+### Environment Synchronization
+
+The `copilot-setup-steps.yml` mirrors tools from `.devcontainer/scripts/on-create.sh` and `.devcontainer/scripts/post-create.sh`. When adding tools to the devcontainer, update the setup workflow to maintain parity.
+<!-- </coding-agent-environment> -->

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

@@ -0,0 +1,64 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: MIT
+#
+# copilot-setup-steps.yml
+# Pre-install tools and dependencies for GitHub Copilot Coding Agent
+# Reference: https://docs.github.com/en/copilot/how-tos/use-copilot-agents/coding-agent/customize-the-agent-environment
+
+name: "Copilot Setup Steps"
+
+# Auto-run on push/PR to validate the setup workflow
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+jobs:
+  # Job MUST be named 'copilot-setup-steps' to be recognized by Copilot
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+
+    # Minimal permissions; Copilot receives its own token for operations
+    permissions:
+      contents: read
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v4.2.2
+        with:
+          persist-credentials: false
+
+      - name: Set up Node.js
+        uses: actions/setup-node@6044e13b5dc448c55e2357c09f80417699197238 # v4.1.0
+        with:
+          node-version: "20"
+          cache: "npm"
+
+      - name: Install JavaScript dependencies
+        run: npm ci
+
+      - name: Set up Python
+        uses: actions/setup-python@39cd14951b08e74b54015e9e001cdefcf80e669f # v5.1.1
+        with:
+          python-version: "3.11"
+
+      - name: Install PowerShell modules
+        shell: pwsh
+        run: |
+          Install-Module -Name PowerShell-Yaml -Force -Scope CurrentUser
+
+      - name: Verify tool availability
+        run: |
+          echo "=== Tool Versions ==="
+          node --version
+          npm --version
+          python3 --version
+          pwsh --version
+          shellcheck --version
+          echo ""
+          echo "=== npm Scripts Available ==="
+          npm run --list