Behavior: Transitions the schedule to a Starting state and initiates channel playback. When background mode is enabled (default), a batch action message is queued for asynchronous processing. When background mode is disabled, the channel is started synchronously.

Authorization: Requires a valid Bearer token.

Side Effects: The schedule status is updated to Starting and a batch action message may be sent. The associated live channel begins playback.

Error Scenarios: Returns 400 if the schedule is not found or is already in a Running, Starting, or Stopping state. Returns 401 if the caller is not authenticated.