swamp-club API: include issue author in GET /api/v1/lab/issues/{number} response

Problem

The GET /api/v1/lab/issues/{number} API endpoint returns issue details (title, body, type, status, comments, assignees) but does not include who created the issue. Comment authors are available via comments[].authorUsername, but the top-level issue object has no author, createdBy, or similar field.

This makes it impossible for tooling to determine whether an issue was filed by a team member or an external contributor — a distinction needed for workflows like co-authoring commits.

Proposed Solution

Add an author/creator field to the issue response object, e.g.:

{
  "issue": {
    "number": 42,
    "author": {
      "userId": "...",
      "username": "..."
    },
    "title": "...",
    ...
  }
}

This would be consistent with how comments[].authorUsername and assignees[].username already surface user identity.

Affected Components

• swamp-club API: GET /api/v1/lab/issues/{number} response shape
• Any downstream consumers that parse the issue response (e.g. the issue-lifecycle extension model's FetchedIssue type)