Streaming char count should display in tool name header, not inline with content

Summary

When a tool is streaming (e.g. Write), the [streaming: N chars] indicator currently renders inline in place of the content parameter value. It would be more useful if this indicator appeared in the tool name / header section instead, so the input block isn't visually disrupted mid-stream.

Current behavior

The streaming char count replaces the parameter value inline:

Write File  hide
  input
  path: reports/promo-video-research.md
  content: [streaming: 12,263 chars]

Suggested behavior

Show the streaming indicator next to the tool name in the header, leaving the input preview area free to render progressively (or remain blank until complete):

Write File  [streaming: 12,263 chars]  hide
  input
  path: reports/promo-video-research.md
  content: ...

This keeps the progress signal visible while the tool header is already the natural place to communicate tool-level state.