Refactor AudioEngine and related components to support token-based authentication for sample loading

Commit notes

- Updated AudioEngine to accept an optional authentication token for fetching samples. - Modified loadTrackSamples method to include parameters for recorded chunks, saved ADSR settings, and selections. - Enhanced SampleManagementProvider and useAudioPlayback hook to utilize the new token functionality. - Adjusted API proxy URL generation in backend to streamline sample download process.