Customer webhook system with CLI management

Features

• Customer webhook system with CLI management
• Configurable send cooldown duration per tenant
• Blog post: Building an Email Pipeline for AI Agents

Fixes

• Fixed SSE stream idle timeout with 15-second heartbeat
• Fixed ioredis dependency for SSE event streaming
• Fixed worker stream event publishing from classify processor via Redis
• Portal SEO audit fixes for sitemap, images, metadata, and cross-linking