A test pins making an app: a bad slug is refused, and a repository that is already an app is not made twice #7132

createApp in src/core/apps.ts refuses invalid_slug and already_app, and no test names them.

Done:

• [ ] A new test: an app is made for a repository with slug shop.
• [ ] Slugs Shop, -shop, a b and an empty string are each invalid_slug.
• [ ] A second app on the same repository is already_app, and the first app's slug and host are unchanged.

Files: test/app-create-refusals.test.ts

If the test finds the behaviour wrong, fix the module it names in the same pull and say so. If the check fails in a test this pull does not touch, name it in the pull rather than widening the change.

Before pushing: bun x tsc --noEmit and the new test.