merge commits

Refactor couchdb-sink: add nested ID template support and helpers

- Add _DocFormatter for {doc.x.y.z} nested field traversal in custom ID templates
- Add get_nested() for dotted-path resolution against dicts
- Add sanitize_id_segment() to strip '/' from CouchDB _ids
- Extend compute_doc_id custom mode with last_updated, last_changed, entity_id tokens
- Update field mode to support dotted paths (e.g. "context.id")

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>