- ToolCard: remove emoji header, collapse Arguments behind <details>,
  render results with structured JSON (color-coded values) or markdown
  detection for string outputs.
- SubagentStep: mirror ToolCard compact layout with same helpers.
- AssistantMessage: fold tool lists when >3 tools — show last 3 + summary
  bar with count and toggle icon-button; TransitionGroup for smooth
  expand/collapse animations.
- Plan card: switch accent color from info to secondary, compact sizing.
- Thinking card: compact sizing, remove bottom margin.
- app.scss: add details::details-content animation, fix nested chevron
  rotation in subagent steps, adjust margins and input-bar padding.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>