add serverless-plugin-split-stacks and update serverless configuration; refactor host function definitions and improve updateHostProfile handler

prisma/schema.prisma

@@ -1,6 +1,7 @@
 generator client {
   provider        = "prisma-client-js"
-  binaryTargets   = ["native", "rhel-openssl-3.0.x"] // Add Linux target
+  engineType      = "binary"
+  binaryTargets   = ["native", "rhel-openssl-3.0.x"] // Lambda Node 18/20 (Amazon Linux) target
   previewFeatures = ["multiSchema"]
 }