Missing labels in setup-labels.yml workflow

The `setup-labels.yml` workflow is missing label definitions for labels that are used in other workflows:

- `pending-coderabbit-review` - used in sync-pr-labels.yml
- `template_sync` - used in template-sync.yml
- `auto_pr` - used in template-sync.yml

These labels should be added to the `requiredLabels` array to ensure all labels are properly provisioned.

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**Related PR:** https://github.com/AOSSIE-Org/SmartNotes/pull/6
**Original comment:** https://github.com/AOSSIE-Org/SmartNotes/pull/6#discussion_r2874000989
**Requested by:** @kpj2006