Added linter.

package.json

@@ -4,7 +4,7 @@
   "description": "A financial tracking web app that allows users to track their investments across multiple exchanges.",
   "main": "index.js",
   "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "lint": "eslint . --fix"
   },
   "author": "",
   "license": "GPL-3.0-or-later",
@@ -14,6 +14,9 @@
   "devDependencies": {
     "@tsconfig/node-lts": "^18.12.5",
     "@types/node": "^20.7.0",
+    "@typescript-eslint/eslint-plugin": "^6.7.3",
+    "@typescript-eslint/parser": "^6.7.3",
+    "eslint": "^8.50.0",
     "typescript": "^5.2.2"
   }
 }