Proxy Hesychia finance webhooks to chat_backend so Stripe POST is not 405.

The static SPA nginx served index.html for /api/finance/webhooks/stripe/ and rejected the method. Closes #41.

roles/web-static/templates/docker-compose.yml.j2

@@ -3,6 +3,9 @@ services:
   web-static:
     image: {{ web_static_image }}
     restart: unless-stopped
+    # Webhook locations proxy to chat_backend on the host-published port.
+    extra_hosts:
+      - "host.docker.internal:host-gateway"
     logging:
       driver: json-file
       options: