ci: auto-close stale issues after 30 days

[liliu-z]

Summary

• Add a scheduled GitHub Actions workflow that automatically closes stale issues
• An issue is closed when the last comment is from a zilliztech org member and there has been no response for over 30 days
• Issues with the keep-open label are exempt from auto-closure
• A comment is posted before closing, informing the user they can reopen or add the keep-open label

How it works

• Runs daily at 02:00 UTC (also supports manual trigger via workflow_dispatch)
• Uses author_association (MEMBER/OWNER) to identify org members — no extra tokens needed
• Only requires issues: write permission with the default GITHUB_TOKEN

Test plan

• Merge to main and verify the workflow appears in the Actions tab
• Manually trigger via workflow_dispatch to test on current open issues
• Verify issues with keep-open label are skipped
• Verify only issues where last comment is from org member and >30 days old are closed

🤖 Generated with Claude Code

[sre-ci-robot]

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This pull-request has been approved by: liliu-z
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