add prettier to backend

backend/package-lock.json

@@ -16,6 +16,7 @@
         "@typescript-eslint/eslint-plugin": "^7.1.1",
         "@typescript-eslint/parser": "^7.1.1",
         "eslint": "^8.57.0",
+        "prettier": "^3.2.5",
         "typescript": "^5.3.3"
       }
     },
@@ -2009,6 +2010,21 @@
         "node": ">= 0.8.0"
       }
     },
+    "node_modules/prettier": {
+      "version": "3.2.5",
+      "resolved": "https://registry.npmjs.org/prettier/-/prettier-3.2.5.tgz",
+      "integrity": "sha512-3/GWa9aOC0YeD7LUfvOG2NiDyhOWRvt1k+rcKhOuYnMY24iiCphgneUfJDyFXd6rZCAnuLBv6UeAULtrhT/F4A==",
+      "dev": true,
+      "bin": {
+        "prettier": "bin/prettier.cjs"
+      },
+      "engines": {
+        "node": ">=14"
+      },
+      "funding": {
+        "url": "https://github.com/prettier/prettier?sponsor=1"
+      }
+    },
     "node_modules/proxy-addr": {
       "version": "2.0.7",
       "resolved": "https://registry.npmjs.org/proxy-addr/-/proxy-addr-2.0.7.tgz",