Fix `ptree(1)` indentation

[basil]

The ptree(1) output does not right-justify process IDs within their indentation level. On illumos, each hierarchy level has a fixed-width column for the PID so that command names align cleanly regardless of PID length. Our implementation left-justifies PIDs, which causes the command column to shift horizontally depending on the number of digits in the PID, producing ragged and harder-to-read output, especially when sibling processes have PIDs of varying lengths.