Document new slash commands

[w287346141]

Summary

• update CLI reference Markdown and static HTML for newly added slash commands in v0.1.6
• add a regression test that requires every registered slash command to appear in both CLI reference artifacts

Commits

• Document new slash commands
• Test CLI reference slash coverage

Validation

• npm.cmd test -- --run tests/carbon-productization.test.ts tests/docs-homepage-style.test.ts
• npm.cmd run verify