[matthewp]

Changes

• Fixes Factory reviews rendering as one big code block (every review on Deduplicate CSS for components used both statically and with client:only on the same page astro#18176). withastro/astro's astro-code-review skill asks for the report "as raw, unrendered Markdown inside a single fenced code block", which suits copying a report by hand. The reviewer carried that plain ``` fence into its submitted summary, and containModelMarkdown only unwrapped fences tagged md/markdown.
• containModelMarkdown now takes unwrapPlainFence, which also strips a plain fence around the whole value. Only whole summaries use it (review summaries and author round summaries). Finding bodies and thread replies keep a plain fenced snippet intact, since there it's usually real code.
• The reviewer prompt now says the summary is published as rendered Markdown and must not be wrapped in a code block, even if the skill asks for one. That covers other repositories' skills with similar report formats.

Testing

• tests/review-markdown.test.ts: a plain fence around a whole summary is unwrapped when asked (backticks and tildes); a plain fenced snippet is kept by default; a plain fence that doesn't wrap the whole value is kept.
• tests/review-diff.test.ts: formatReviewBody renders a summary shaped like the #18176 reviews as headings below the verdict notice, with no code fence.

Docs

• No docs update needed.