Header, message action, send/stop, history, model selector and dark-mode controls had no accessible name (icon-only buttons). Adds roles/labels and selected/disabled state; no visual change.
MessageBubble CC 19 -> below 10. The fence and indented code block rules were identical and are now one CodeBlock component; the Markdown style map lives in markdownStyles.ts. Adds characterization tests for the bubble (roles, actions visibility, edited badge, copy feedback).
evandro