Deleting a label in Administration > Labels removes it from every work package without a trace in the activity. Each affected work package should record the removal.

**Acceptance criteria**

* When an admin deletes a label that work packages carry, every affected work package gets an activity entry authored by that admin: "**Label Begin of the insertionremoved:** 'Frontend'End of the insertion Begin of the deletion removed** because the label '<name>'End of the deletion was Begin of the insertiondeleted".
* Several labels deleted byEnd of the insertion Begin of the deletion deleted", together withEnd of the deletion the Begin of the insertionsame admin within the journal aggregation window show as one entry: "**Label removed:** 'Frontend', 'Backend', 'Middleware' were deleted".
* The entry does not show a "Labels changed" line; the removedEnd of the insertion labels Begin of the insertionare named in the cause.End of the insertion Begin of the deletion detail ("Labels: A, (deleted label)" to "A").End of the deletion
* The entries are written by a background job after the deletion; the admin is not kept waiting. Re-running the job adds no duplicate entries.
* Labels nobody uses (including the never-used inline labels removed nightly by COMMS-1050) produce no entries.

**Technical notes**

* Begin of the insertionJournalEnd of the insertion Begin of the deletion New journalEnd of the deletion cause `label_deleted` (`Journal::CausedByLabelDeletion`) carrying Begin of the insertion`label_ids`End of the insertion Begin of the deletion `label_id`End of the deletion and Begin of the insertion`label_names`,End of the insertion Begin of the deletion `label_name`,End of the deletion since the label Begin of the insertionrows areEnd of the insertion Begin of the deletion row isEnd of the deletion gone when the journal is written; rendered through Begin of the insertion`OpenProject::JournalFormatter::Cause` with pluralisation.End of the insertion Begin of the deletion `OpenProject::JournalFormatter::Cause`.End of the deletion
* Begin of the insertion`Journals::CreateService` aggregates a cause into the predecessor's journal when the cause declares `aggregatable_with?` / `aggregate_with` (no-op defaults on `CauseOfChange::Base`); the label deletion cause merges the lists.
* End of the insertion `Labels::DeleteService` collects the work package ids before destroying the label and enqueues `Labels::JournalizeDeletionJob`, which calls `Journals::CreateService` per work package under the work package mutex (no notifications). Begin of the insertion
* The activities tab hides the labels detail on entries with this cause; API details are unchanged.End of the insertion
* Depends on label journaling (COMMS-1022, PR #25320). Sibling of COMMS-1050 (PR #26187).