Link Zendesk tickets to existing Jira issues both ways

**Objective:** Link Zendesk ticket {ticket-id} to the existing Jira issue {issue-key} so both records point at each other.

**Step 1: Confirm both records exist**

Call `zendesk-get-ticket` with ticket-id {ticket-id} and `jira-get-issue` with issue-key {issue-key}. If either is missing, report which and stop.

**Step 2: Check for an existing link**

Call `zendesk-get-ticket-comment` with ticket-id {ticket-id} and public false. If a note starts `Linked Jira issue: {issue-key}`, report that they are already linked and stop.

**Step 3: Confirm, then write**

Show the user the ticket subject and the issue summary side by side and wait for confirmation. Then:

1. Call `zendesk-add-ticket-comment` with ticket-id {ticket-id}, public false, and a body whose first line is `Linked Jira issue: {issue-key}`, followed by the issue summary and status.
2. Call `jira-add-issue-comment` on {issue-key} with the Zendesk ticket id, subject, requester organization and priority.
3. If {zendesk-subdomain} is not empty, call `jira-add-issue-remote-link` with url https://{zendesk-subdomain}.zendesk.com/agent/tickets/{ticket-id}, title Zendesk ticket {ticket-id}, application-name Zendesk and global-id zendesk-ticket-{ticket-id}.

**Step 4: Report**

Which writes succeeded, and that this issue will be found from the ticket but not from Jira-side searches by `[ZD-{ticket-id}]`, because its summary was not changed.

**Rules & Guidelines:**

* `zendesk-get-ticket`, `zendesk-get-ticket-comment` and `zendesk-add-ticket-comment` are on the zendesk server. `jira-get-issue`, `jira-add-issue-comment`, `jira-add-issue-remote-link` and `jira-get-issue-watcher` are on the jira server.
* Do not rename the Jira issue with `jira-update-issue` and do not call `zendesk-update-ticket`. The Zendesk note must have public false.
* Linking convention used by every prompt on this server: an escalated Jira issue's summary starts with `[ZD-<ticket id>]`, and the Zendesk ticket carries an internal note whose first line is `Linked Jira issue: <ISSUE-KEY>`. Find links by either marker.
* Jira issue ids: `jira-get-issue` returns the issue key but not the numeric id. Pass the key (e.g. ABC-123) where a Jira tool asks for an issue id; Jira accepts either. If Jira rejects the key, call `jira-get-issue-watcher` filtered by issue-key and take its issue-id.

**Validation:**

* If the Zendesk note succeeds and the Jira comment fails, report the half-made link so the user can retry only the Jira side.