Don't throw in interaction service when no inputs

[JamesNK]

Description

Fix issue when canceling input dialog.

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 prevents InteractionService from throwing when an inputs dialog is dismissed and adds a test to cover the cancel scenario.

• Removed the exception throw in CompleteInteractionAsync when result.State is null for inputs interactions.
• Added a new xUnit test (WatchInteractions_PromptInputAsync_CompleteOnCancelResponse) to verify that cancelling an input dialog completes without data.
• Cleaned up a duplicate using Aspire.DashboardService.Proto.V1; in the test file.

Reviewed Changes

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

File	Description
src/Aspire.Hosting/ApplicationModel/InteractionService.cs	Removed the InvalidOperationException for null input state
tests/Aspire.Hosting.Tests/Dashboard/DashboardServiceTests.cs	Added a test for canceling an inputs dialog and cleaned up imports