Color theme: allow custom colors for custom octal permission groups

Like you can color differently read/write in the `rwx` format would be nice if you could color `0755` differently from `0644`
A simple user-definable number→color matching filter could work

Start by locating the Rust CLI's existing color handling for rwx permissions and the configuration path for user-defined colors. Compare how octal permissions such as 0755 and 0644 are rendered, then verify that a number-to-color mapping can distinguish them and that the existing rwx behavior remains unchanged.

Written by the indexing model from the issue text.