Add Copilot setup steps workflow

Adds a dedicated GitHub Actions workflow to provide environment context for GitHub Copilot. It installs the required .NET SDK versions (8.x, 9.x, and 10.x) and restores dependencies to ensure Copilot has a valid build state for the toolkit.

Author: Keboo

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

@@ -0,0 +1,39 @@
+name: "Copilot Setup Steps"
+
+# Automatically run the setup steps when they are changed to allow for easy validation, and
+# allow manual testing through the repository's "Actions" tab
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+defaults:
+  run:
+    shell: pwsh
+
+jobs:
+  # The job MUST be called `copilot-setup-steps` or it will not be picked up by Copilot.
+  copilot-setup-steps:
+    runs-on: windows-latest
+
+    permissions:
+      contents: read
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v6
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v5
+        with:
+          dotnet-version: |
+            8.x
+            9.x
+            10.x
+
+      - name: Restore dependencies
+        run: dotnet restore MaterialDesignToolkit.Full.slnx