Social Backlog Sweep

Sweep historical claimed activities into the social cross-post webhook.

Selection criteria (must ALL hold):

• status != 'cancelled'
• visibility = 'public'
• claim_status = 'claimed'
• anonymized = false
• date_time between (now - past_days) and (now + upcoming_days)

Each candidate is sent to the same webhook used on activity create (Make.com / Zapier / etc.). dry_run=true returns the candidate list only.

Reuses crosspost_activity() so the privacy filter and payload shape stay in lock-step with the live publish path.