Add instructions and env setup for Copilot (#4869)

Taken from #4866

Author: premun

.github/copilot-instructions.md

@@ -1,8 +1,12 @@
+## Coding Guidelines
 - Rules apply to our C# code.
 - Use function-reflective, descriptive names without implementation details.
+- Avoid magic strings and numbers; use constants or configuration.
 - For multi-task methods, use descriptive names and document the process.
 - Long method names are acceptable.
+- Prefer async/await over Task.Result or .Wait()
 - Async methods must have an "Async" suffix.
+- Use cancellation tokens for async operations when appropriate
 - Avoid using booleans solely to signal success, unless failure is an expected frequent outcome (e.g. TryGet methods).
 - Do not return null unless explicitly indicated (e.g., TryCreate).
 - Validate early; if validation fails, throw or return immediately.
@@ -11,4 +15,28 @@
 - Use immutable objects (e.g., records, readonly properties) when possible.
 - Never throw generic Exceptions.
 - Use structural logging consistently.
-- Each method should log its own actions.
+- Each method should log its own actions.
+- Use nullable reference types and annotate appropriately.
+- Follow the AAA (Arrange-Act-Assert) pattern for unit tests.
+- Prefer ILogger<T> over ILogger for better context in logs.
+- Services should be registered with appropriate lifetimes (singleton, scoped, transient).
+
+## Repository Structure
+- `docs/` - Documentation
+- `eng/` - Engineering scripts, build tools and pipeline templates
+- `src/` - Contains the main source code for arcade services
+- `test/` - Test projects and test utilities
+- `Microsoft.DotNet.Darc/` - Darc CLI tool for interacting with dependency management services
+
+## Key Technologies
+- .NET 8
+- Azure DevOps APIs
+- ASP.NET Core for web APIs
+- Entity Framework Core for data access
+- Azure Container Apps for hosting
+- .NET Aspire for local development
+
+## Development Environment
+- You can restore required .NET and dependencies by calling:
+  - `./eng/common/build.sh -restore` on Linux/macOS
+  - `.\eng\common\build.ps1 -restore` on Windows

.github/copilot-setup-steps.yml

@@ -0,0 +1,15 @@
+name: Copilot Setup Steps
+
+# These steps will be executed before GitHub Copilot assists with code
+# This helps ensure Copilot has access to properly restored dependencies
+
+steps:
+- name: Checkout repository
+  uses: actions/checkout@v3
+  with:
+    fetch-depth: 0
+
+- name: Restore dependencies
+  run: |
+    ./eng/common/build.sh -restore
+  shell: bash