Documentation gaps that block theming

Problem/Motivation

docs/presentation.md omits --act-color-danger, --act-indent, --act-indent-cap, and --act-bubble-inset, the last three being the only lever a themer has for indentation. The claim that all custom properties are consumed with fallbacks is false (comment.css:42 and :62), and that is the direct cause of the escaping bubble tail in Issue F. Neither doc mentions the SDC replaces: contract, which is the only supported way to swap the card markup, so a themer reading the docs concludes it is immutable. There is also no caveat that enabling Authored by / Authored on display components on the comment view mode duplicates the card byline.

Steps to reproduce

• Read docs/presentation.md and attempt to theme indentation or swap the card markup; note the missing tokens and the undocumented replaces: contract.

Proposed resolution

• Document the four omitted tokens and correct the fallback claim.
• Document the SDC replaces: contract for swapping the card markup.
• Document the byline duplication caveat when Authored by / Authored on display components are enabled.

Remaining tasks

• Verify the corrected claims against the current CSS.

User interface changes

None; documentation only.

API changes

None anticipated.

Data model changes

None anticipated.

AI-Generated: Yes (Used Opus 5 and DeepSeek Flash to review and discover these issues)