Spend Management: Realtime Usage Alerts, SMS Notifications, and Project Pausing

Introduced Spend Management features including email/web/SMS notifications for spend thresholds, flexible webhooks for real-time usage updates, and automatic project pausing. Added APIs for programmatic project pausing/resuming. Updated Vercel Functions to support up to 5-minute durations on Pro plans (15 on Enterprise) with safer 15-second defaults, building on previous recursion protection.