fix(webapp): stop slow database cleanup on project deletion

[d-cs]

Summary

Deleting a project triggered an unbounded database cleanup that scanned the project's entire run history, so deleting a project with many runs could be very slow. Project deletion is a soft delete again: run data is retained and the deletion completes quickly.

Fix

Project deletion ran a cascade hard-delete whose BulkActionItem step filtered through a relation to TaskRun scoped by projectId. Prisma compiles that to an EXISTS-join over the project's entire TaskRun set (a large, hot table with no projectId index), and it ran on every project deletion unconditionally.

Removing the cascade-cleanup call restores the prior soft-delete behaviour: queues are removed, the project is marked deleted, and run data is retained. The cascade-cleanup service (added in #4117) had no other callers, so it and its test are deleted.

[coderabbitai]

Walkthrough

Project deletion no longer performs a hard-delete cascade cleanup of run-ops data across run-ops databases. The RunOpsCascadeCleanupService and its call site in the project deletion service were removed, along with its dedicated integration test suite. A related comment in the archive branch service was reworded to remove a direct reference to the removed service, pointing instead to a general purge runbook. A changelog entry documents the fix, noting that project deletion previously could hang for projects with many runs due to slow database cleanup.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description covers the summary and fix, but it misses the required Closes line, testing steps, changelog, screenshots, and checklist items.	Add the missing template sections: Closes #issue, completed checklist, testing details, changelog summary, and screenshots or an explicit note if none.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title is concise and accurately describes the main change to stop slow cleanup on project deletion.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/deleteproject-soft-delete-remove-runops-cascade

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[devin-ai-integration]

Devin Review found 1 potential issue.