docs: move the third Loop Agent label back into the Loop box

The Agent C outline for the Loop Agent column is a copy of the Parallel
column's label and relied on a separate transform to sit in the Loop box.
That line was removed before #2249 merged, so the Loop box renders empty.
Shift the path's starting point instead, so the position no longer depends
on an extra attribute. The rest of the path is relative, so only the first
coordinate changes.

Author: vishal-bulbule