Persist push subscriptions to disk, add background NWS alert poller

docker-compose.yml

@@ -8,6 +8,14 @@ services:
     environment:
       - PORT=3005
       - NODE_ENV=production
+      # Required for push notifications — generate with: npx web-push generate-vapid-keys
+      - VAPID_PUBLIC_KEY=${VAPID_PUBLIC_KEY:-}
+      - VAPID_PRIVATE_KEY=${VAPID_PRIVATE_KEY:-}
+      - VAPID_SUBJECT=${VAPID_SUBJECT:-mailto:nate@necloud.us}
+      # Optional: how often to poll NWS alerts (ms). Default: 300000 (5 min)
+      # - ALERT_POLL_INTERVAL_MS=300000
+    volumes:
+      - ./data:/app/data
     healthcheck:
       test: ["CMD", "wget", "-qO-", "http://localhost:3005/"]
       interval: 30s