Tenant deletion from the admin dashboard

Features

• Tenant deletion from the admin dashboard
• All agent endpoints consolidated under /v1/agent for a cleaner API
• Per-tenant quotas page in the admin dashboard
• Session-based auth for analytics endpoints in the portal
• Upgraded Starter and Growth plan limits with custom domain caps
• Comprehensive API reference integration tests

Fixes

• Fixed login sessions not persisting on Vercel
• Fixed retry loop errors causing send failures
• Fixed sent tab showing trashed and archived threads
• Fixed permanent delete errors and magic link tenant provisioning
• Fixed domain listing errors and outbound proxy auth
• Fixed routing confidence floor to reduce false approval escalations
• Fixed database migration for unique constraints