Configure PM2 for single instance to prevent sync conflicts

- Change from cluster mode with max instances to single fork instance
- Add ENABLE_BACKGROUND_SYNC=false to prevent accidental sync in web processes
- Guarantee no competing processes ever exist

Author: Jon-edge

pm2.json

@@ -3,8 +3,11 @@
     {
       "name": "ratesServer",
       "script": "lib/index.js",
-      "instances" : "max",
-      "exec_mode" : "cluster",
+      "instances": 1,
+      "exec_mode": "fork",
+      "env": {
+        "ENABLE_BACKGROUND_SYNC": "false"
+      },
       "error_file": "/var/log/pm2/ratesServer.error.log",
       "out_file": "/var/log/pm2/ratesServer.out.log"
     },