Add failure label to "AutoBuilder - Failed" notifications for recent build failures

[Copilot]

NotificationService immediately closes any issue without the failure label. QueueBuildCommand only added this label on exceptions, not when the category was "Failed" due to recent build failures — so "AutoBuilder - Failed" issues were created and immediately closed.

Changes

• QueueBuildCommand.cs: Changed the AppendIf condition from exception is not null to category == "Failed", which covers both failure paths (exceptions and recent build failures):

// Before
}.AppendIf(NotificationLabels.Failure, () => exception is not null),

// After
}.AppendIf(NotificationLabels.Failure, () => category == "Failed"),

• QueueBuildCommandTests.cs: Added QueueBuildCommand_RecentFailedBuilds_IncludesFailureLabel test and a VerifyNotificationLabelsContain helper on TestContext.

[Copilot]

Pull request overview

This pull request fixes notification triage for AutoBuilder failures by ensuring GitHub issues created for “AutoBuilder - Failed” states consistently include the failure label, preventing NotificationService from auto-closing them.

Changes:

• Update QueueBuildCommand to add the failure label whenever the notification category is "Failed" (covers both exceptions and recent-failure throttling).
• Add a new unit test asserting the failure label is included when builds are skipped due to too many recent failures.
• Introduce a TestContext helper to verify notification labels.

Reviewed changes

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

File	Description
src/ImageBuilder/Commands/QueueBuildCommand.cs	Adjusts failure-label assignment logic to align with the "Failed" notification category.
src/ImageBuilder.Tests/QueueBuildCommandTests.cs	Adds coverage for recent-failure throttling notifications including the failure label, plus a label-verification helper.