Add per-message copy button to VSCode extension

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Please add per-message copy button just after the chat message to VSCode extension.

Proposed Solution

<img width="267" height="152" alt="Image" src="https://github.com/user-attachments/assets/a3db4939-dd89-450b-a04a-21ba96354f22" />

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_