fix: add explicit permissions to auto-close workflow (strands-agents#893)

- Add permissions block with minimal required permissions
- Resolves CodeQL security issue actions/missing-workflow-permissions
- Follows principle of least privilege with contents:read, issues:write, pull-requests:write

🤖 Assisted by Amazon Q Developer

Author: Unshure

.github/workflows/auto-close.yml

@@ -11,6 +11,11 @@ on:
         default: 'false'
         type: boolean
 
+permissions:
+  contents: read
+  issues: write
+  pull-requests: write
+
 jobs:
   auto-close:
     runs-on: ubuntu-latest