Behavior: Finalizes the multipart upload by combining all uploaded parts into the final asset file. This triggers post-upload processing including media analysis, transcoding, AI detection, and search indexing. Call this only after all parts have been uploaded and confirmed via the complete-part endpoint.

Authorization: Requires a valid Bearer token.

Side Effects: The uploaded parts are assembled into the final file. Asynchronous processing jobs (transcoding, AI analysis, indexing) are triggered.

Error Scenarios: Returns 401 if the caller is not authenticated.