recording: Use the current session render node consistently across recording
KPipeWire currently chooses GPU/render devices in multiple places independently (VAAPI selection, DMA-BUF handling, modifier negotiation). On hybrid systems this can lead to inconsistent GPU selection across the recording pipeline.
This change introduces a shared session render-node resolver and uses the current session render node consistently for:
- VAAPI device selection
- DMA-BUF import path
- stream modifier negotiation