feat: what is new since my last visit, and turning a comment into a ticket

Opening a ticket notes the visit and answers the one before (issue_visits),
so the page marks others' comments and changes since. A comment can become
a ticket of its own, as a subtask or linked; it remembers where it went.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/infrastructure/src/lib/graphql/fragments.graphql

@@ -218,6 +218,10 @@ fragment CommentFields on Comment {
   resolvedBy {
     ...UserRefFields
   }
+  spawned {
+    id
+    key
+  }
   createdAt
   editedAt
   author {