Complete the mandatory receiver-consent gate that was wired in the
backend but never connected to the UI callback chain:
- Add the missing onIncomingFileRequest (4th) callback to
setFileTransferCallbacks in app.jsx — its absence caused
handleFileTransferStart to auto-reject every incoming file.
- Remove independent callback registration from FileTransferComponent;
the component was overwriting app-level callbacks on mount and
nulling all four on unmount, silently breaking progress/received/
error handlers whenever the panel was hidden.
- Lift pendingIncomingFiles state to the root component so consent
prompts are shown regardless of panel visibility; auto-open the
panel on incoming request.
- Add getReceivedFileObjectURL / revokeReceivedFileObjectURL on
EnhancedSecureWebRTCManager for download buttons in the panel.
- Update file-transfer-ui-cleanup regression test to match the new
single-owner callback architecture.
- All 14 tests pass; clean production build.