Add Copilot coding agent environment setup workflow (#373)

Configures the GitHub Copilot coding agent development environment to
enable AI-assisted coding in this repository.

## Changes

- **Created `.github/workflows/copilot-setup-steps.yml`**
  - Job named `copilot-setup-steps` (required by Copilot)
  - Minimal permissions: `contents: read`
  - Triggers on workflow_dispatch, push/PR to the workflow file itself

- **Reused existing CI components**
  - `actions/checkout@v4` from dotnetBuild.yml
- `actions/setup-dotnet@v4` with `global-json-file: "./global.json"`
from dotnetBuild.yml
  - `dotnet restore` command from dotnetBuild.yml

The workflow prepares a .NET 8.0 environment with restored dependencies
before Copilot begins work, following the [official GitHub documentation
pattern](https://docs.github.com/en/enterprise-cloud@latest/copilot/how-tos/use-copilot-agents/coding-agent/customize-the-agent-environment).

<!-- START COPILOT ORIGINAL PROMPT -->



<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>Customizing the development environment for GitHub
Copilot coding agent</issue_title>
>
<issue_description>https://docs.github.com/en/enterprise-cloud@latest/copilot/how-tos/use-copilot-agents/coding-agent/customize-the-agent-environment
> 
> Sample:
> ```
> 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
> 
> jobs:
> # The job MUST be called `copilot-setup-steps` or it will not be
picked up by Copilot.
>   copilot-setup-steps:
>     runs-on: ubuntu-latest
> 
> # Set the permissions to the lowest permissions possible needed for
your steps.
>     # Copilot will be given its own token for its operations.
>     permissions:
> # If you want to clone the repository as part of your setup steps, for
example to install dependencies, you'll need the `contents: read`
permission. If you don't clone the repository in your setup steps,
Copilot will do this for you automatically after the steps complete.
>       contents: read
> 
> # You can define any steps you want, and they will run before the
agent starts.
>     # If you do not check out your code, Copilot will do this for you.
>     steps:
>       - name: Checkout code
>         uses: actions/checkout@v5
> 
>       - name: Set up Node.js
>         uses: actions/setup-node@v4
>         with:
>           node-version: "20"
>           cache: "npm"
> 
>       - name: Install JavaScript dependencies
>         run: npm ci
> 
> ```
> 
> Reuse/share components from our existing CI pipelines where we
can</issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>



<!-- START COPILOT CODING AGENT SUFFIX -->

- Fixes #372

<!-- START COPILOT CODING AGENT TIPS -->
---

💬 We'd love your input! Share your thoughts on Copilot coding agent in
our [2 minute survey](https://gh.io/copilot-coding-agent-survey).

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: BenjaminMichaelis <22186029+BenjaminMichaelis@users.noreply.github.com>

Author: Copilot

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

@@ -0,0 +1,37 @@
+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
+
+jobs:
+  # The job MUST be called `copilot-setup-steps` or it will not be picked up by Copilot.
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+
+    # Set the permissions to the lowest permissions possible needed for your steps.
+    # Copilot will be given its own token for its operations.
+    permissions:
+      # If you want to clone the repository as part of your setup steps, for example to install dependencies, you'll need the `contents: read` permission. If you don't clone the repository in your setup steps, Copilot will do this for you automatically after the steps complete.
+      contents: read
+
+    # You can define any steps you want, and they will run before the agent starts.
+    # If you do not check out your code, Copilot will do this for you.
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v4
+        with:
+          global-json-file: "./global.json"
+
+      - name: Restore dependencies
+        run: dotnet restore