Add initial project structure with configuration and sample files

- Create .envrc for Direnv configuration
- Add .pre-commit-config.yaml for pre-commit hooks
- Include CONTRIBUTING.md with contribution guidelines
- Implement Makefile for build, run, and clean commands
- Set up Program.cs with a basic Hello World message
- Define SampleApp.csproj for .NET project configuration
- Add agents.md for coding agent instructions
- Create default.nix for Nix flake setup
- Initialize deps.nix for NuGet dependencies
- Configure Flatpak app with app.flatpak.json
- Implement install-templates.sh for installing .NET templates
- Define project.toml for project metadata
- Set up shell.nix for development shell environment
- Add SampleTest.cs for basic unit testing

agents.md

@@ -0,0 +1,16 @@
+# Coding Agent Instructions
+
+This project is intended for educational purposes. To support this, please adhere to the following guidelines:
+
+## Allowed Actions
+- **Environment Maintenance:** Feel free to update Nix flakes, shell configurations, or other environment-related setup.
+- **Project Housekeeping:** Maintain a standard project layout, keep `README.md` up-to-date, and clean up temporary or build-related files.
+- **Documentation:** Add comments, manage project documentation, and add links to relevant external resources.
+
+## Restricted Actions
+- **Source Code Editing:** You are NOT allowed to edit the executable source code (project root) except to improve documentation..
+- **Code Generation:** Do not provide example code unless explicitly asked by the user.
+
+## Communication Guidelines
+- **Educational Focus:** When asked about code, prioritize explaining the concepts and providing advice over writing code.
+- **Documentation Links:** Always include links to official language or library documentation for references.