Replace stale preset max slash copy

[w287346141]

Summary

• replace stale user-facing /preset max slash guidance with the current /preset pro name
• update docs source copy, /pro localized feedback, and related comments
• add a slash regression test so /pro keeps pointing users at /preset pro

Validation

• git grep -n "/preset max|preset max" -- docs src README.md README.zh-CN.md returned no matches
• npm.cmd test -- --run tests/slash.test.ts tests/slash-help-i18n.test.ts tests/carbon-productization.test.ts
• push hook ran npm.cmd run verify