[Feature]: Show PRs and issues differently in chat link chips

[MartinPTielemans]

Before submitting

• I searched existing issues and did not find a duplicate.
• I am describing a concrete problem or use case, not just a vague idea.

Area

apps/web

Problem or use case

Chat turns GitHub PR and issue references into chips that all show the same GitHub logo. In the chat, a PR and an issue look the same, even though:

• they're different kinds of thing, and
• they open in different places. PR links open in T3 Code's right panel, but issue links open the system browser.

Nothing tells you which one you're clicking until you've clicked it.

Proposed solution

• Use GitHub's own icons for the type: the pull-request icon for /pull/N, the issue icon for /issues/N. The URL path already says which it is, so no API call is needed.
• Optional: colour the icon by state, the way GitHub does (open green, merged purple, closed red or grey). This could reuse the snapshot data linked PRs already have.
• Until issues open in the app (feat(issues): link issues to threads and expose issue tools to agents #19270), add a small ↗ to chips that open in the browser.

Smallest useful scope

Just the icon split. The state colours and ↗ can come later.

Related

• feat(issues): link issues to threads and expose issue tools to agents #19270 (issue URLs in chat open the issue panel)
• [Feature]: Make the default action for file and pull request links configurable #11403 (configurable click action for PR links)