CVE-2026-33678: Vikunja has IDOR in Task Attachment ReadOne Allows Cross-Project File Access and Deletion

Vikunja is an open-source self-hosted task management platform. Prior to version 2.2.1, `TaskAttachment.ReadOne()` queries attachments by ID only (`WHERE id = ?`), ignoring the task ID from the URL path. The permission check in `CanRead()` validates access to the task specified in the URL, but `ReadOne()` loads a different attachment that may belong to a task in another project. This allows any authenticated user to download or delete any attachment in the system by providing their own accessible task ID with a target attachment ID. Attachment IDs are sequential integers, making enumeration trivial. Version 2.2.1 patches the issue.