Add support for markdown formatting in interaction message

[JamesNK]

Description

Add support for markdown content in the message.

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire-docs issue (consider using one of the following templates):
      • New (or update) doc-idea template
      • New breaking-change template
      • New diagnostic template
  • No

[Copilot]

Pull Request Overview

This PR adds support for rendering interaction messages as Markdown throughout the dashboard components.
Key changes include:

• Introducing a message_as_markdown flag in the proto and propagating it through the hosting service.
• Adding a new MarkdownHelpers utility and initializing a pipeline in the Blazor provider to convert Markdown to sanitized HTML.
• Extending the public API (InteractionOptions), component view models, dialogs, and unit tests to cover Markdown scenarios.

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/Aspire.Dashboard.Components.Tests/Interactions/InteractionsProviderTests.cs	Add theory-based tests for Markdown vs. plain-text message rendering.
src/Aspire.Hosting/Dashboard/proto/dashboard_service.proto	Introduce message_as_markdown field in WatchInteractionsResponseUpdate.
src/Aspire.Hosting/Dashboard/DashboardService.cs	Map InteractionOptions.MessageAsMarkdown into the response update.
src/Aspire.Hosting/ApplicationModel/IInteractionService.cs	Add nullable MessageAsMarkdown property to InteractionOptions.
src/Aspire.Dashboard/Utils/MarkdownHelpers.cs	New helper class to build a Markdig pipeline and convert Markdown.
src/Aspire.Dashboard/Model/InteractionsInputsDialogViewModel.cs	Add required Message property for pre-rendered HTML content.
src/Aspire.Dashboard/Components/Interactions/InteractionsProvider.cs	Initialize Markdown pipeline, render messages with GetMessageHtml.
src/Aspire.Dashboard/Components/Dialogs/InteractionsInputDialog.razor	Render the formatted Message as MarkupString in the dialog.
src/Aspire.Dashboard/Aspire.Dashboard.csproj	Reference the Markdig package.
playground/Stress/Stress.AppHost/InteractionCommands.cs	Update example commands to demonstrate Markdown usage.
eng/Signing.props	Add Markdig.dll to the signing configuration.
THIRD-PARTY-NOTICES.TXT	Include license notice for Markdig.
Directory.Packages.props	Pin Markdig package version.

Comments suppressed due to low confidence (2)

src/Aspire.Hosting/ApplicationModel/IInteractionService.cs:329

• Add XML documentation with <remarks> and <code> sections for this new public API property to match the existing style and fulfill the API review checklist.

    public bool? MessageAsMarkdown { get; set; }

src/Aspire.Dashboard/Model/InteractionsInputsDialogViewModel.cs:18

• Consider adding a triple-slash summary comment for the new Message property to explain that it contains pre-rendered HTML from Markdown.

    public required string Message { get; init; }

[davidfowl]

cc @captainsafia

[mitchdenny]

Tested this out in the codespace and works as advertised. Markdown actually supports HTML which I did try about but I noticed we don't render it :) Understandable given the conversations that we've had in the background. Thanks for doing this.