Format root GitHub repository links in chat

[hideoneric]

Raw GitHub repository URLs are visually noisy in the composer and in sent user messages.

I propose formatting canonical repository-root URLs as a compact GitHub icon plus owner/repository, while preserving the original URL for sending, copying, draft restoration, and navigation. Issue, pull request, file, and other deeper GitHub URLs would keep their existing rendering.

This is a web-client presentation change and therefore applies to the desktop wrapper as well. It does not change providers, server contracts, remote connection behavior, or mobile rendering.

Before	After

Implementation PR: #9634