Vikunja: Link-share principal-type confusion enables cross-account team removal, bot takeover, and roster disclosure

Summary Vikunja's web.Auth interface pkg/web/web.go, single method GetID int64 is satisfied by BOTH user.User and models.LinkSharing. A link-share's GetID returns the raw positive share.ID pkg/models/linksharing.go:83-85, which lives in the same positive autoincrement ID space as users.id. The sa...