feat(davinci-client): add QRCode collector support

Add QR_CODE field type support to the DaVinci client SDK,
enabling applications to render QR codes returned by DaVinci flows.

- Add QrCodeField type and QrCodeCollectorBase interface
- Add returnQrCodeCollector factory with defensive fallbacks
- Wire QR_CODE dispatch in node reducer (early return, same as LABEL)
- Export QrCodeCollector in public API types
- Add QR code component and config to sample davinci-app
- Add unit tests for factory and reducer integration [Self-Healing CI Rerun]

Author: nx-cloud[bot]