CVE-2026-117649: Gitea private issue disclosure through issue dependency timeline events

The issue timeline API and the web issue page hid cross-reference events that point at issues the reader cannot access, but not "dependency added" and "dependency removed" events. When a readable issue had been linked as a dependency to an issue in a repository the reader cannot access, for example a private repository, any reader of the first issue, including anonymous users of a public repository, received the linked issue's current title, body, state, labels, poster and attachment names through the API, and its repository, number and title on the web page. Creating the link requires access to both issues; comments and attachment downloads of the linked issue stayed protected. Dependency events are now filtered with the same read permission check; a related exposure of unlinked attachment metadata through hidden dependency placeholders was already fixed in 28.2.0.