fix: use server-side timestamp for instance-started log entry

[AlekseyManetov]

Closes #86

Proposed Changes

The instance-started log entry used a client-side Date.now() timestamp captured when the HTTP response arrived, which could be later than the server-side element instance timestamps for fast tasks (e.g. script tasks), causing wrong entry ordering. Fixed by preferring the server-side process instance startDate from the polled result when available, falling back to the client timestamp before the first poll.

Before:

After:

Checklist

Ensure you provide everything we need to review your contribution:

• Your contribution meets the definition of done
• Any new additions or modifications are consistent with the existing UI and UX patterns
• Pull request description establishes context:
  • Link to related issue(s), i.e. Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}
  • Brief textual description of the changes
  • Screenshots or short videos showing UI/UX changes
  • Steps to try out, i.e. using the @bpmn-io/sr tool

[nikku]

Let's move this to the place where we set the polled result (ExecutionLog#setPolledResult).

[AlekseyManetov]

Fixed