da-live deletion guards

1. Show how many files are about to be deleted: We can crawl the selected file/folder list and get a count to display to the user.
2. Prevent deletion of 10,000 files at once.
3. Do not allow user to delete non-draft content if they do not have write permissions to .trash - This might be problematic though, and require consumers with complicated access rights to have to also rights to the .trash dir

Start from the da-live deletion flow and the selected file/folder list described in the issue. Trace how deletion requests are handled, then define completion as showing the pending file count, blocking batches of 10,000 or more, and enforcing the stated .trash permission rule without leaving the access-rights question unresolved.

Written by the indexing model from the issue text.