Fix errors when extending song

[tmirkovic]

Was getting errors when trying to extend a song.

Invalid Request Errors

Request would fail with:

Error extend audio: {"detail":"Invalid request. Inconsistent task and generation params"}

Adding task: 'extend' to payload to match Suno client seems to resolve issue

Unauthorized Errors

Another issue would happen only when extend song route was called first before other routes:

Error extend audio: {"detail":"Unauthorized"}

Likely same issue as described here:
#172
#71

Resolved by calling keepAlive before extend song request

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