Switch backend to wait for SQL Server and use direct INSERTs

Replace stored procedure calls with inline INSERT statements and
SCOPE_IDENTITY()
Add netcat for readiness check in new entrypoint.sh
Introduce dedicated SQL Server and init-db services in docker-compose

docker-compose.yml

@@ -1,14 +1,39 @@
 services:
+  sql:
+    image: mcr.microsoft.com/mssql/server:2022-latest
+    container_name: sql
+    environment:
+      - ACCEPT_EULA=Y
+      - SA_PASSWORD=Ou812@12!@
+    ports:
+      - "1433:1433"
   backend:
     build:
       context: ./backend
       dockerfile: Dockerfile
+    depends_on:
+      - sql
     container_name: backend
     environment:
-      - DB_SERVER=homelab.local
+      - DB_SERVER=sql
       - DB_USER=sa
       - DB_PASSWORD=Ou812@12!@
       - DB_NAME=CustomerDB
     ports:
       - "8080:8080"
     command: ./main
+    extra_hosts:
+      - "homelab.local:192.168.1.129"
+
+  init-db:
+    build:
+      context: ./db
+      dockerfile: Dockerfile
+    container_name: init-db
+    depends_on:
+      - sql
+    environment:
+      - DB_SERVER=sql
+      - DB_USER=sa
+      - DB_PASSWORD=Ou812@12!@
+      - DB_NAME=CustomerDB