linear.createIssueComment adds a top-level comment or threaded reply.
automations/comment-on-linear-issue.automation.ts
issueId and a non-empty Markdown body. Optional parentId creates a threaded reply. Set doNotSubscribeToIssue: true to avoid automatically subscribing the acting user. Optional second argument { account } defaults to the project binding.
Returns the created LinearComment. Keep its id for update or deletion.