Schedule Uploaded Contacts

Trigger OTTR scheduling for all contacts in awaiting_scheduling status.

This endpoint processes all contacts across all campaigns that are in 'awaiting_scheduling' status. It uses Thompson sampling to assign optimal next_follow_up_date_time values and transitions contacts to 'awaiting_contact'.

The scheduling process:

1. Fetches contacts in batches of 1000
2. Groups by campaign_id and timezone
3. Gets optimal hour distribution via Thompson sampling
4. Samples a specific time for each contact
5. Updates contacts to awaiting_contact status with scheduled time

Returns: ScheduleUploadResponse with counts and processing time