Note

Fix chat timeline row height estimation to account for markdown, work groups, diff summaries, and proposed plans

• Replaces estimateTimelineMessageHeight with a unified estimateTimelineRowHeight in MessagesTimeline.tsx that handles message, work, proposed-plan, and working row kinds.
• Adds markdown-aware height estimation for assistant messages: normalizes text for wrapping, applies per-element bonuses for headings, lists, blockquotes, tables, and fenced code blocks.
• Adds dynamic height estimation for work rows (grouped entries, overflow, file chips), diff summary sections (tree node count), and proposed plan rows (collapsible preview cap).
• Introduces resolveMessagesTimelineRows in MessagesTimeline.logic.ts to precompute row state including completion divider flags, assistant diff summaries, and grouped work entries.
• Adds browser-based height parity tests in MessagesTimeline.browser.tsx that mount the real component, measure DOM row heights, and assert they match estimator output within per-kind tolerances.

^{Macroscope summarized 28fad63.}