Owner notification webhook: Telegram re-point (#23)

Flask fires a fire-and-forget internal webhook (owner_notify.py, mirroring
mailer.py's background-thread queue) on booking create/cancel/reschedule,
carrying the same {booking, business_name, notify_channel} shape the old
EA-driven "Build booking row" node produced, plus an event field so the
Telegram message can say what actually happened. n8n/booking-sync.json gets
a new webhook + IF node feeding the existing Telegram node directly, so it
no longer needs EA's API to build the notification payload; channel routing
(only telegram sends for now) lives in that IF node.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backoffice/docker-compose.yml

@@ -32,6 +32,7 @@ services:
       SMTP_PASSWORD: ${SMTP_PASSWORD}
       MAIL_FALLBACK_FROM: ${MAIL_FALLBACK_FROM}
       PUBLIC_BASE_URL: ${PUBLIC_BASE_URL}
+      OWNER_NOTIFY_WEBHOOK_URL: ${OWNER_NOTIFY_WEBHOOK_URL}
     depends_on:
       smb-db:
         condition: service_healthy