Auto-generate HMAC-SHA256 webhook secret when enabling the Gaiia
integration. Display webhook URL, secret with copy buttons, regenerate
option, and setup instructions on the integrations page.
Replace the thundering-herd cron job with a dispatcher that enqueues
individual per-integration Oban jobs staggered across the 10-minute
window using PollingOffset. Show last synced timestamp in user's
local timezone via the <.timestamp> component.
