Use proper 'duplicate' state_reason for issue closures

- Update auto-close script to use state_reason: 'duplicate' instead of 'not_planned'
- Simplify workflow detection logic to only check for duplicate state_reason
- Remove fallback logic for backward compatibility - use modern GitHub API

🤖 Generated with [Claude Code](https://claude.ai/code)

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

.github/workflows/log-issue-events.yml

@@ -115,14 +115,10 @@ jobs:
             CLOSED_AUTOMATICALLY="true"
           fi
           
-          # Check if closed as duplicate by looking for duplicate label or state_reason
+          # Check if closed as duplicate by state_reason
           CLOSED_AS_DUPLICATE="false"
-          if [ "$STATE_REASON" = "not_planned" ]; then
-            # Check if issue has duplicate label
-            LABELS=$(echo "$ISSUE_DATA" | jq -r '.labels[] | select(.name | test("duplicate"; "i")) | .name')
-            if [ -n "$LABELS" ]; then
-              CLOSED_AS_DUPLICATE="true"
-            fi
+          if [ "$STATE_REASON" = "duplicate" ]; then
+            CLOSED_AS_DUPLICATE="true"
           fi
           
           # Prepare the event payload

scripts/auto-close-duplicates.ts

@@ -65,7 +65,7 @@ async function closeIssueAsDuplicate(
     'PATCH',
     {
       state: 'closed',
-      state_reason: 'not_planned',
+      state_reason: 'duplicate',
       labels: ['duplicate']
     }
   );