Workflow to check stale assigned issues

This workflow runs daily and checks for issues that have been assigned
for over two weeks without any activity from the assignee. It will post
a reminder comment if:

- The issue has an assignee
- No comments from the assignee in the last 2 weeks
- No linked pull requests
- No recent bot reminders

The workflow can also be triggered manually for testing purposes.

[ci skip]

Co-Authored-By: Claude <noreply@anthropic.com>