Copilot response links: add right-click Copy Path for files and folders

## Scenario

I use VS Code desktop with **Copilot** selected as the session type, rather than **Local**.

When Copilot returns a link to a file or folder, I want to right-click it and copy its path. I cannot currently do that from the response link.

## Requested behavior

Add **Copy Path** to the right-click menu for file and folder links in Copilot responses. Copy the filesystem path as plain text so I can paste it into another conversation or handoff.

## Why this matters

Copying file and folder paths is a common part of my handoffs. I want to keep the clickable link and also be able to copy its path directly.

## Related report

#280165 covers copying file references from responses into external systems. This request is specifically for a right-click **Copy Path** command, rather than changing how an entire response copies.

## Environment

VS Code desktop, Copilot session type. Exact VS Code build not yet collected.