Bootstrap Event Subscription System

Set up a complete event-driven notification system in a Phoenix 1.8 application with:

• Event struct and PubSub-based event bus
• Database-backed event subscriptions (email, SMS, webhook channels)
• Listener GenServer for orchestrating delivery
• PgFlow jobs for email, SMS, webhook, and in-app delivery
• Notification delivery logging
• Webhook signing (Standard Webhooks spec)
• LiveView real-time integration
• Multi-tenant account scoping

Prerequisites:

• Phoenix 1.8+ application with PostgreSQL and binary_id primary keys
• PgFlow already configured (bootstrap-phoenix Phase 7 / /pgflow bootstrap)
• Swoosh already configured for email
• An accounts table with binary_id primary key
• A users table with email and optionally phone fields
• Phoenix.PubSub already in supervision tree