fix: handle null user in comment transform

[ralfschimmel]

Summary

Fix crash when transforming issues that contain comments with user: null.

Problem

When running linearis issues update (or read) on an issue that has comments created by Linear's Agent Protocol, the CLI crashes with:

Cannot read properties of null (reading 'id')

Stack trace:

TypeError: Cannot read properties of null (reading 'id')
    at GraphQLIssuesService.doTransformIssueData (graphql-issues-service.js:577:38)

Root Cause

Linear's Agent Protocol creates system comments (e.g., "This thread is for an agent session with bobbin.") where user is null. The transform code at line 889-892 assumes comment.user always exists:

user: {
  id: comment.user.id,      // Fails when comment.user is null
  name: comment.user.name,
},

Example Data That Fails

From the raw API response, these comments have user: null:

{
  "id": "ec4c235a-f2f3-4650-abfa-587bb51610ef",
  "body": "This thread is for an agent session with bobbin.",
  "createdAt": "2025-12-28T12:13:47.400Z",
  "updatedAt": "2025-12-28T12:18:06.594Z",
  "user": null
}

Fix

1. Made user optional in LinearComment interface (user?: instead of user:)
2. Added null-check in transform, following the same pattern used for assignee:

user: comment.user
  ? {
      id: comment.user.id,
      name: comment.user.name,
    }
  : undefined,

Testing

After the fix, issues with agent protocol comments are processed correctly. Comments with null users simply omit the user field in the output.

🤖 Generated with Claude Code

[ralfschimmel]

Closing - will resubmit with only the bugfix commit (accidentally included unrelated feature commits)