Make worker delay configurable via appsettings.json

Refactored Worker to accept IConfiguration and read the delay interval from "Worker:DelayMilliseconds" in appsettings.json, replacing the previously hardcoded value. This allows the worker execution interval to be configured without code changes. Added a minimum delay safeguard and updated appsettings.json accordingly.

EnvelopeGenerator.ServiceHost/appsettings.json

@@ -5,5 +5,8 @@
       "Microsoft.AspNetCore": "Warning"
     }
   },
+  "Worker": {
+    "DelayMilliseconds": 1000
+  },
   "AllowedHosts": "*"
 }