.NET: Update AG-UI samples for latest MAF + AG-UI SDK and align with docs

[Daniel Roth (danroth27)]

Motivation & Context

The .NET AG-UI samples had diverged from the current MAF integration, AG-UI C# SDK, and Learn documentation. The human-in-the-loop sample maintained custom approval middleware despite native approval and resume support, while the state-management sample emitted DataContent that the released AG-UI server did not map to state events. Several clients also replayed messages already retained by AgentSession, and one frontend tool exposed a compiler-generated name.

This update makes the samples accurate references for streaming chat, backend and frontend tools, human approval, multi-turn sessions, and shared state.

Description & Review Guide

• What are the major changes?
  • Update all AGUI.* packages from 0.0.3 to 0.0.4.
  • Simplify Steps 01-03 and give the frontend location tool the stable get_user_location name.
  • Replace Step04's custom client/server approval middleware with ApprovalRequiredAIFunction, ToolApprovalRequestContent.CreateResponse, and the native AG-UI resume flow.
  • Replace Step05's custom state middleware and DataContent output with RunAgentInput.State, a thin state-context agent, and AGUIStreamOptions.MapResultAsStateSnapshot.
  • Let AgentSession exclusively own prior conversation history so clients send only each new turn.
  • Refresh the AG-UI sample README for the shipped APIs, ports, security guidance, and behavior.
• What is the impact of these changes?
  • The samples now demonstrate supported first-class APIs instead of protocol workarounds.
  • Approval/resume, frontend and backend tools, multi-turn memory, and shared-state snapshots work end to end.
  • All ten sample projects build cleanly, and the targeted AG-UI unit and integration suites pass.
• What do you want reviewers to focus on?
  • The native approval/resume loop in Step04.
  • The state input and declarative snapshot mapping in Step05.
  • The ownership boundary between each client's current-turn messages and AgentSession history.

Related Issue

Fixes #7623

Related documentation update: MicrosoftDocs/semantic-kernel-docs#430

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.

[Copilot]

Pull request overview

This PR simplifies the .NET AG-UI Step04 “Human-in-the-loop” sample by removing the bespoke server/client approval-middleware layer and relying on the framework’s native tool-approval interrupt + resume flow when using ApprovalRequiredAIFunction.

Changes:

• Removes the custom server-side DelegatingAIAgent that translated approval requests/responses to a bespoke request_approval tool-call protocol.
• Removes the custom client-side DelegatingAIAgent and JSON plumbing used to marshal the bespoke approval protocol.
• Updates the Step04 server and client to map/use the underlying agents directly (MapAGUIServer("/", baseAgent) and chatClient.AsAIAgent(...)).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
dotnet/samples/02-agents/AGUI/Step04_HumanInLoop/Server/ServerFunctionApprovalServerAgent.cs	Deletes custom server approval middleware and its custom JSON-serialized approval models.
dotnet/samples/02-agents/AGUI/Step04_HumanInLoop/Server/Program.cs	Removes custom JSON options + wrapper agent; maps the base agent directly via MapAGUIServer.
dotnet/samples/02-agents/AGUI/Step04_HumanInLoop/Client/ServerFunctionApprovalClientAgent.cs	Deletes custom client approval middleware and its custom approval models.
dotnet/samples/02-agents/AGUI/Step04_HumanInLoop/Client/Program.cs	Uses the AGUI-backed agent directly and removes now-unneeded custom approval-agent wiring.