Shorten thread route from /thread to /t

All internal links (tiles, prev/next nav, comments, notifications,
breadcrumb, dropzone route check) point to /t/<id>. A global route
middleware permanently redirects old /thread/<id> URLs including
query string and comment anchor.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/plugins/notifications.client.ts

@@ -54,7 +54,7 @@ export default defineNuxtPlugin(() => {
             description: n.content?.slice(0, 80) || undefined,
             action: {
               label: $i18n.t('notifications.view'),
-              onClick: () => navigateTo(`/thread/${n.uploadId}#comment-${n.commentId}`),
+              onClick: () => navigateTo(`/t/${n.uploadId}#comment-${n.commentId}`),
             },
           })
         }