Upgrade project to .NET 9 with updated dependencies, documentation, and CI/CD

[Copilot]

This PR upgrades the ToDo App Template from .NET 8 to .NET 9, bringing the project up to the latest stable version of the .NET ecosystem.

Changes Made

Framework Upgrade

• Updated all project files to target net9.0 instead of net8.0
• Updated Dockerfile to use .NET 9 base images (mcr.microsoft.com/dotnet/aspnet:9.0-alpine and mcr.microsoft.com/dotnet/sdk:9.0)
• Updated GitHub workflow (CI) to use .NET 9 (dotnet-version: 9.0.x)

Package Updates

• Entity Framework Core: Upgraded from 8.0.x to 9.0.8

  • Microsoft.EntityFrameworkCore → 9.0.8
  • Microsoft.EntityFrameworkCore.Design → 9.0.8
  • Npgsql.EntityFrameworkCore.PostgreSQL → 9.0.4
  • EFCore.NamingConventions → 9.0.0

• Microsoft Extensions: Updated all Microsoft.Extensions packages from 8.0.0 to 9.0.8

  • Configuration abstractions, binder, dependency injection, and HTTP client packages

• Other Dependencies:

  • MediatR: 12.2.0 → 13.0.0
  • Fluid.ViewEngine: 2.5.0 → 2.25.0
  • FastEndpoints packages: 5.21.2 → 5.30.0 (maintained API compatibility)

Documentation & Tooling

• Updated README.md to reference .NET 9 instead of .NET 8
• Updated prerequisites section to point to .NET 9 download page
• Verified dotnet-ef tool compatibility with .NET 9 (version 9.0.8)

Bug Fixes

• Removed broken project reference to non-existent DZarsky.ToDoAppTemplate.Domain.csproj that was causing build warnings

Verification

✅ All projects build successfully without errors
✅ Entity Framework migrations and database commands work correctly
✅ Application starts and runs (database connection failures are expected without PostgreSQL)
✅ Docker build configuration updated and compatible
✅ GitHub workflow updated to use .NET 9 for CI builds
✅ All package dependencies resolve correctly

Compatibility Notes

The upgrade maintains full backward compatibility. There are 2 minor deprecation warnings in the FastEndpoints library, but these don't affect functionality. The FastEndpoints version was kept at 5.30.0 to avoid breaking API changes that would require code modifications.

This upgrade brings improved performance, security updates, and access to the latest .NET 9 features while maintaining the existing codebase structure.

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[Loupeznik]

@copilot change the dotnet versions in CI (github workflows) as well

[Loupeznik]

@copilot change the dotnet versions in CI (github workflows) as well

[Copilot]

@copilot change the dotnet versions in CI (github workflows) as well

Updated the GitHub workflow to use .NET 9 in commit 792654b. The build.yml workflow now uses dotnet-version: 9.0.x to match the project upgrade.

[Copilot]

@copilot change the dotnet versions in CI (github workflows) as well

Updated the GitHub workflow to use .NET 9 in commit 792654b. The build.yml workflow now uses dotnet-version: 9.0.x to match the project upgrade.