Discord embeds render markdown, not HTML — the PR Reviewer Guide table
(<table><tr><td>…) was appearing as literal HTML in the webhook message.
Added htmlToDiscordPlain(): collapses the table into readable lines
(score/effort/security/key-issues), keeps emoji + **bold** markdown, and
decodes entities. Also fixed review score suffix '/10' → '/100' (the LLM
score scale is 0-100, matching the table's 'Score: 72').