- If client_id is missing or null in sync request, derive it from ClientActivity table
- Look up most recent client activity for the API token to get rustdesk_id
- Use derived client_id throughout the sync process (ReportSync, Bet, ExtractionStats, MatchReport)
- Prevents database error: 'Column client_id cannot be null'
- Ensures server uses same client identifier that client uses
- Returns client_id_used in response for debugging
- Fixes issue where client sends null client_id but server needs valid identifier