docs(s02): explain why specialized tools are needed when Bash can do the same work

In s02, Bash can already read, write, edit, and find files. As a learner, I was confused about why the agent adds read_file, write_file, edit_file, and glob.

I suggest adding a short explanation: specialized tools do not add new capability, but provide structured inputs, reduce shell quoting errors, and make future permission and logging policies more precise.

This will be a documentation-only change.