feat(autofix): Add copy PR URL button and open icon to pull request card (#112358)

Add *Open-in-new-tab icon** — adds the `IconOpen` icon to the View PR
LinkButton, matching the pattern already used in CodingAgentCard for
external links.

Before:
<img width="1538" height="274" alt="CleanShot 2026-04-07 at 14 46 21@2x"
src="https://github.com/user-attachments/assets/4609ad62-5c17-4ce8-94fb-f8d7713b91e9"
/>

After:
<img width="1468" height="262" alt="CleanShot 2026-04-07 at 14 56 45@2x"
src="https://github.com/user-attachments/assets/262095fe-2db4-4ee6-b383-6f228ad9e37e"
/>

Agent transcript:
https://claudescope.sentry.dev/share/Y_Qw59GBniE1Wx444uIuXMxOWycGEXk17h2cdAJWP6U

Author: chromy

static/app/components/events/autofix/v3/autofixCards.tsx

@@ -280,7 +280,12 @@ export function PullRequestsCard({section}: AutofixCardProps) {
         ) {
           return (
             <Flex key={pullRequest.repo_name} gap="xs" align="center">
-              <LinkButton external href={pullRequest.pr_url} priority="primary">
+              <LinkButton
+                external
+                href={pullRequest.pr_url}
+                priority="primary"
+                icon={<IconOpen />}
+              >
                 {t('View %s#%s', pullRequest.repo_name, pullRequest.pr_number)}
               </LinkButton>
               <Button