Add Docker Compose and backend Dockerfile

Include .gitignore, go.mod/go.sum, initial Go source, init.sql, and
Docker‑Compose
configuration for the MSSQL and backend services.

docker-compose.yml

@@ -0,0 +1,33 @@
+services:
+  mssql:
+    image: mcr.microsoft.com/mssql/server:2019-latest
+    container_name: mssql
+    environment:
+      - SA_PASSWORD=Passw0rd
+      - ACCEPT_EULA=Y
+    ports:
+      - "1433:1433"
+    volumes:
+      - ./db/data:/var/opt/mssql
+
+  backend:
+    build:
+      context: ./backend
+      dockerfile: Dockerfile
+    container_name: backend
+    depends_on:
+      - mssql
+    environment:
+      - DB_SERVER=mssql
+      - DB_USER=sa
+      - DB_PASSWORD=Passw0rd
+      - DB_NAME=CustomerDB
+    ports:
+      - "8080:8080"
+    volumes:
+      - ./backend:/app
+    command: ./main
+
+networks:
+  default:
+    driver: bridge