VS Code extension: pinned first message hides conversation when long

Description

In the VS Code extension, the first message in a conversation appears to be pinned/stuck at the top of the chat panel. When this first message is long (e.g., invoking a skill with detailed context), it takes up most of the visible area and pushes the rest of the conversation out of view.

Steps to Reproduce

1. Open Claude Code in VS Code extension
2. Send a long first message (e.g., a /debug-scan-rule skill invocation with full rule details, context, and related links)
3. Claude responds and the conversation continues
4. The first message remains pinned at the top, taking up significant vertical space
5. The actual conversation (Claude's responses and follow-up messages) is hidden below the fold

Expected Behavior

The first message should either:

• Be collapsible/expandable so users can minimize it after reading
• Have a max height with scroll, so it doesn't dominate the panel
• Not be pinned, and scroll naturally with the rest of the conversation

Actual Behavior

The first message stays pinned at the top at full height, hiding the ongoing conversation. Users must scroll past it every time to see Claude's responses.

Environment

• VS Code Claude Code extension
• Linux (WSL2)