feat: initial raven-notify — Discord + email alerts via POST /notify

FastAPI at port 8400. Both channels fire on every notification.
Grafana webhook endpoint ready for later wiring.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,17 @@
+services:
+  raven:
+    build: .
+    container_name: raven-notify
+    restart: unless-stopped
+    ports:
+      - "8400:8400"
+    volumes:
+      - /opt/sites:/opt/sites
+      - /opt/agent-os:/opt/agent-os
+    env_file: .env
+    networks:
+      - proxy
+
+networks:
+  proxy:
+    external: true