Add repository agent guidelines

[KSemenenko]

Summary

• add an AGENTS.md file at the repository root to outline contribution expectations

Testing

• not run (not required)

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Codex Task

[Copilot]

Pull Request Overview

This PR upgrades the Orleans.RateLimiting library from .NET 8 to .NET 9, updating all dependencies to their latest versions and modernizing the CI/CD pipeline.

• Migrates all projects to target .NET 9.0
• Updates Orleans dependencies from 8.1.0 to 9.2.1
• Replaces FluentAssertions test library with Shouldly
• Modernizes GitHub Actions workflows with new CI, CodeQL, and Release pipelines

Reviewed Changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
README.md	Updates documentation to reflect .NET 9 targeting, fixes spelling errors (Attributes, middleware), adds build instructions and CI badges
ManagedCode.Orleans.RateLimiting.Tests/ManagedCode.Orleans.RateLimiting.Tests.csproj	Migrates to .NET 9.0 and updates all test dependencies including Orleans 9.2.1, ASP.NET Core 9.0.10, xunit 2.9.3/3.1.5, and adds Shouldly 4.2.1
ManagedCode.Orleans.RateLimiting.Tests/*.cs	Replaces FluentAssertions syntax with Shouldly assertions across all test files
ManagedCode.Orleans.RateLimiting.Server/ManagedCode.Orleans.RateLimiting.Server.csproj	Updates to .NET 9.0 and Orleans 9.2.1 dependencies
ManagedCode.Orleans.RateLimiting.Core/ManagedCode.Orleans.RateLimiting.Core.csproj	Updates to .NET 9.0 and Orleans 9.2.1 dependencies
ManagedCode.Orleans.RateLimiting.Client/ManagedCode.Orleans.RateLimiting.Client.csproj	Updates to .NET 9.0, Orleans 9.2.1, and ManagedCode.Communication 9.6.5
ManagedCode.Orleans.RateLimiting.Client/Middlewares/OrleansBaseRateLimitingMiddleware.cs	Corrects Result.Fail parameter order to match updated ManagedCode.Communication 9.6.5 API
Directory.Build.props	Bumps package version from 0.0.8 to 0.0.9 and updates DotNet.ReproducibleBuilds to 1.2.39
AGENTS.md	Adds new agent guidelines document for development standards
.github/workflows/release.yml	Adds comprehensive new release workflow with NuGet publishing and GitHub release automation
.github/workflows/ci.yml	Adds new CI workflow replacing the old dotnet.yml workflow
.github/workflows/codeql-analysis.yml	Modernizes CodeQL workflow with updated actions and .NET 9 support
.github/workflows/nuget.yml	Removes old NuGet workflow (replaced by release.yml)
.github/workflows/dotnet.yml	Removes old .NET workflow (replaced by ci.yml)

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[chatgpt-codex-connector]

Align xUnit runner with xUnit package version

The test project still references xunit 2.9.3 while xunit.runner.visualstudio was bumped to 3.1.5. The 3.x Visual Studio runner is designed for xUnit.net v3 and is not compatible with v2 test assemblies, which means test discovery/execution in CI or Visual Studio will fail or skip all tests. Either revert the runner back to the latest 2.x release or upgrade the whole test suite to xUnit v3 so the tooling versions match.

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