[WIP] Fix tool result markdown rendering for JSON arrays

## Investigation Plan

### Problem Statement
Tool results that are JSON arrays of objects (e.g., `[{"type": "text", "text": "## Heading\n\nParagraph"}]`)
are NOT rendering the markdown content properly. The text values within the JSON objects should be
parsed and displayed as formatted markdown (headers, paragraphs, lists, etc.).

### Current Behavior
- JSON arrays are detected
- But the text content within is shown as raw text, not rendered markdown

### Expected Behavior
- Each "text" value in content blocks should be rendered as proper markdown
- Headers should display as `<h2>`, `<h3>`, etc.
- Lists should display as `<ul>/<li>`
- Code blocks should have syntax highlighting

### Tasks
1. Review PR comments for relevant feedback
2. Analyze current `render_content_block_array()` implementation
3. Fix markdown parsing within JSON text values
4. Fix subagent functionality issues
5. Add/update tests
6. Verify on ShlomoStept/claude-code-transcripts fork ONLY

IMPORTANT: All work on ShlomoStept fork only. NO pushes to simonw/upstream.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: ShlomoStept