Add option to skip initial comment informing about code review is in progress

When the code review starts with `track_progress: true`, Claude makes a comment similar to

```
Claude Code is working… claude-thinking.gif

I'll analyze this and get back to you.
```

which triggers an email to the PR author.

It would be great if there is an option to tell Claude to not to post this initial comment.

Start by tracing how the `track_progress: true` option triggers the initial review comment and where action options are defined. Add a user-configurable way to suppress that comment while leaving the rest of the code review in progress, and verify that the option preserves normal review behavior.

Written by the indexing model from the issue text.