.NET: Add Foundry Agent Skills sample

[Seáic Mac Murchadha (seaic-mac-murchadha)]

Motivation & Context

Adds the Foundry Agents sample requested in #4006 for using Agent Skills with a server-side versioned Foundry agent.

Description & Review Guide

• What are the major changes?
  • Add Agent_Step27_AgentSkills under the Foundry Agents samples.
  • Demonstrate defining an AgentInlineSkill and exposing it through AgentSkillsProvider.
  • Inject the skills provider into a versioned FoundryAgent through clientFactory.
  • Configure read-only Agent Skills operations for auto-approval.
  • Add the sample README and register the sample in the Foundry sample index and .NET solution.
• What is the impact of these changes?
  • Adds a Foundry Agents example for using Agent Skills with a server-side versioned agent.
  • No changes to existing runtime or library behavior.
• What do you want reviewers to focus on?
  • Whether the clientFactory composition is the preferred pattern for using AgentSkillsProvider with a versioned FoundryAgent.

Related Issue

Fixes #4006 (Foundry Agents)

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.

Note: New sample builds ran with 0 warnings or errors. Unit tests were N/A, as this change is step only.

[Copilot]

🟡 Changes recommended

The fixed agent name can cause cleanup to delete another run’s or an existing agent’s versions.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds a .NET sample demonstrating Agent Skills with a server-side versioned Foundry agent.

Changes:

• Defines an inline support-policy skill with read-only auto-approval.
• Demonstrates clientFactory integration and agent cleanup.
• Registers and documents the sample.

File summaries

File	Description
foundry/README.md	Adds the sample to the index.
Agent_Step27_AgentSkills/README.md	Documents setup and execution.
Agent_Step27_AgentSkills/Program.cs	Implements the sample.
Agent_Step27_AgentSkills.csproj	Configures dependencies.
agent-framework-dotnet.slnx	Registers the project.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Balanced

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[Copilot]

🟢 Approval recommended

The focused sample is complete, consistent with surrounding patterns, and introduces no unresolved issues.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 0 new
• Review effort level: Balanced