chore: add GitHub Actions workflow to auto-remove status:* labels on issue close

[vmvarela]

Description

Action item from Sprint 1 Retrospective (#70).

Several closed issues in Sprint 1 retained status:ready, status:in-progress, status:blocked, or status:review labels after being closed. Add a GitHub Actions workflow that automatically removes all status:* labels when an issue is closed.

Acceptance Criteria

• Workflow triggers on issues: [closed] event
• Removes labels: status:ready, status:in-progress, status:blocked, status:review
• Only acts if the issue actually has one of those labels (no-op otherwise)
• Workflow added to .github/workflows/