Add annotation/comment syntax

[akonan]

Description

Support annotations and comments in wireframes for design notes.

Proposed Syntax

[Submit] <!-- This should be primary CTA -->

## Hero {.annotation="Needs approval from design team"}

::: note
This section is pending final copy from marketing.
:::

Features

• Inline comments (not rendered in HTML)
• Visual annotations (rendered as notes/tooltips)
• Design decision documentation
• TODO markers
• Version notes

Rendering

• Show annotations in special mode: --show-annotations
• Hide by default in production renders
• Include in JSON output

Priority

Low

Labels

enhancement, annotations, syntax