fix(api): cancel builds on template delete

[jakubno]

Cancel active template builds when deleting template

[cursor]

PR Summary

Medium Risk
Touches template deletion and build-cancellation flow, plus changes the DeleteTemplate query return shape; mistakes could leave builds running or cause partial cleanup/cancellation failures.

Overview
Template deletion now also cancels any in-progress builds for the deleted template by extending DeleteTemplate to return both alias keys and active build metadata (build/node/cluster) and invoking orchestrator build deletion with a timeout. Snapshot cleanup and cache invalidation were updated to handle the new DeleteTemplate return type, and the unused DeleteActiveTemplateBuild SQL/query was removed with tests adjusted accordingly.

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

There are 3 total unresolved issues (including 2 from previous reviews).

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