[FEATURE] VS Code extension: click-to-copy affordance on code blocks in Claude responses

Summary

In the Claude Code VS Code extension, code blocks rendered in Claude's responses have no click-to-copy affordance. Copying requires manually selecting the text with the mouse, which is slow and error-prone for multi-line snippets.

Current behavior

When Claude outputs a fenced code block in the VS Code extension chat panel, the block renders with syntax highlighting but no copy button and no click-to-copy behavior. To copy a snippet I have to click, drag-select the full range, then Cmd+C.

Expected behavior

Either (or both) of:

1. Copy button on hover — a small copy icon appears in the top-right of the code block when hovered, click to copy the full contents, with a brief "Copied" confirmation.
2. Click-anywhere-to-copy — clicking anywhere inside the block copies its contents and shows a brief "Copied" confirmation.

This matches the convention in the Claude.ai web app, GitHub, ChatGPT, and essentially every modern chat UI that renders code.

Why it matters

Copy-paste from Claude into the editor is one of the primary workflows in the extension. Missing the copy affordance is currently the biggest ergonomic gap compared to both the web app and competing coding assistants.

Environment

• Claude Code VS Code extension
• macOS (Darwin 25.3.0)