.NET: Enable Valkey NuGet package publishing

[Copilot]

Motivation & Context

Microsoft.Agents.AI.Valkey was blocked from being published as a NuGet package due to an explicit <IsPackable>false</IsPackable> override. It also wasn't included in the release solution filter, so it was excluded from publish pipelines.

Description & Review Guide

• What are the major changes?

  • Removed <IsPackable>false</IsPackable> (and its associated comment) from Microsoft.Agents.AI.Valkey.csproj, allowing it to inherit IsPackable=true from the central nuget-package.props.
  • Added Microsoft.Agents.AI.Valkey to agent-framework-release.slnf in alphabetical order alongside the other publishable packages.

• What is the impact of these changes? The Valkey package will now be packed and published as a NuGet artifact in release builds.

• What do you want reviewers to focus on? Confirm the VersionSuffix=alpha in the csproj is the intended pre-release label for the initial publish.

Related Issue

Closes #7058

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.

[westey-m]

CC @MatthiasHowellYopp

[Copilot]

Pull request overview

This PR enables Microsoft.Agents.AI.Valkey to be produced as a NuGet package in release builds by removing its explicit non-packable override and ensuring it is included in the release solution filter used by publish pipelines.

Changes:

• Removed the project-level <IsPackable>false</IsPackable> override so Valkey inherits IsPackable=true from dotnet/nuget/nuget-package.props.
• Added Microsoft.Agents.AI.Valkey to dotnet/agent-framework-release.slnf so it participates in release packing/publishing.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
dotnet/src/Microsoft.Agents.AI.Valkey/Microsoft.Agents.AI.Valkey.csproj	Removes the explicit pack-blocker so the project is eligible for NuGet packing via central props.
dotnet/agent-framework-release.slnf	Includes the Valkey project in the release solution filter used for publish flows.