.NET: Fixes for bug bash.

[westey-m]

Motivation and Context

Description

• A few small bug bash fixes.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

Updates a few .NET GettingStarted samples to address bug-bash feedback by clarifying expected runtime behavior and adjusting sample instructions/output.

Changes:

• Clarified chat-reduction sample behavior by adding additional chat history inspections and updating the follow-up prompt.
• Adjusted persisted-conversation sample to avoid temp-file roundtrip and instead display serialized session data, then resume the session.
• Updated MCP Inspector README command to explicitly run the sample under net10.0.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
dotnet/samples/GettingStarted/Agents/Agent_Step16_ChatReduction/Program.cs	Adds explanatory comments and extra history checks to illustrate when reduction occurs.
dotnet/samples/GettingStarted/Agents/Agent_Step10_AsMcpTool/README.md	Updates inspector command to include --framework net10.0 to match the project’s target.
dotnet/samples/GettingStarted/Agents/Agent_Step06_PersistedConversations/Program.cs	Switches from temp-file persistence demo to console output + immediate session resume; adds CA1869 suppression.