Soft-delete a time entry and detach its associated time blocks.

Returns the soft-deleted entry (deleted_at populated) plus every detached child block — blocks stay live with time_entry_id cleared, so they return to the unattached/pending pool instead of being discarded. Both carry the trigger-advanced version. The desktop client applies the response directly to its local SQLite mirror; the next GET /api/v1/sync round re-delivers the same rows and the version-check predicate makes the second apply a no-op. Released time entries cannot be deleted.