Integration deletion is very slow on uninstall

[sentry-junior]

Summary

Deleting a Sentry app integration (clicking "Uninstall" on a configuration) is very slow — it does not complete instantly as expected. The operation takes a noticeably long time, making the UI feel unresponsive.

Symptom

• Navigate to an installed integration's configuration page
• Click "Uninstall" / delete the integration
• Deletion is slow; the user waits several seconds (or longer) before the operation completes

Expected behavior

Deletion should be near-instant or at minimum provide responsive feedback. The API call triggering deletion is likely synchronous and blocking on work that could be deferred (e.g. cascading deletes, async cleanup tasks).

Root cause hypotheses

• High confidence: Deletion endpoint performs synchronous cascading cleanup (e.g. uninstalling webhooks, revoking tokens, cleaning up installations) in the request/response cycle rather than deferring to a background task.
• Medium confidence: The SentryApp or SentryAppInstallation deletion path may be doing database-level cascades or firing external API calls inline.

Unknowns

• Exact endpoint and view handling the delete request
• Whether there is any task deferral currently in place
• Scale of the slowdown (seconds vs. tens of seconds; consistent or variable by integration)

Action taken on behalf of David Cramer.

[linear-code]

ENG-7259

[sentry-junior]

Additional context from further testing: the deletion is async (not sync), and takes several minutes to complete. This creates a particularly painful loop for integration testing/development — uninstalling, waiting minutes for deletion to process, then attempting reinstall is severely disruptive. The reinstall flow may also incorrectly show the app as still installed while deletion is pending (tracked separately in #112441).

[sentry-junior]

Additional context from someone who tested this flow: the uninstall runs on an interval every 10–15 minutes in batches (not immediately), which makes the dev/testing reinstall loop even worse. You're basically stuck waiting a full batch cycle between each uninstall/reinstall attempt with no indication of when the deletion will actually clear.