fix: resolve transaction rollback and duplicate key errors in blog update flow

Problems fixed:
- Transaction was rolling back silently due to writeDump() and abort calls inside
  the transaction block, and helper functions swallowing errors with return false
  instead of rethrowing them
- deleteBlogTags() and deleteBlogCategories() were using Wheels soft delete,
  leaving rows physically in the database, causing duplicate key violations on
  the unique_blog_tag and unique_blog_category constraints when saveTags() and
  saveCategories() attempted to re-insert the same associations
- findOne() on the Tag model was not using includeSoftDeleted=true, so
  soft-deleted tags were invisible to Wheels but still present in the DB,
  causing "Name has already been taken" validation errors on re-save

Author: zainforbjs