docs(argcheck): address PR review comments

Problem
- PR review comments pointed out unclear shape descriptions, awkward wording in auto selection, and missing line breaks in  bullet lists.

Change
- use explicit  shape descriptions for dipole and polarizability labels
- replace "wrapped up to 4 divisible" with "rounded up to a multiple of 4" throughout
- add explicit line breaks to  bullet lists and improve related wording

Authored by OpenClaw (model: custom-chat-jinzhezeng-group/gpt-5.4)

Author: njzjz-bot