fix(copilot): render markdown in CAD progress notes and thin the timeline scrollbar

[devin-ai-integration]

Summary

The CAD tool progress panel was showing raw Markdown (e.g. **Considering design details**) and the timeline had the default chunky scrollbar.

• Markdown now accepts an optional inline prop that renders paragraphs as <span> so progress snippets can be embedded in single-line, truncated rows.
• CadProgressLine renders progress.note as inline Markdown.
• CadProgressTimeline renders each entry.note as Markdown and styles its <ol> with scrollbar-width: thin and a muted track color.
• Added unit tests for Markdown and enabled Vitest's automatic JSX transform so UI components can be tested with react-dom/server.

Link to Devin session: https://app.devin.ai/sessions/d846e91524fc43aca04de9649aeb2300
Requested by: @alanshen27

[devin-ai-integration]

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[devin-ai-integration]

The checks failure is the same two pre-existing phase0-journey E2E failures that are also failing on the latest main run (run 31055824031):

• e2e/phase0-journey.spec.ts:21:5 › full Phase 0 journey
• e2e/phase0-journey.spec.ts:109:5 › chat channels and visual CAD parameters

Unit tests, lint, and typecheck pass locally and in CI. The E2E failures appear unrelated to this UI-only change.