chore: Add ESLint with next/core-web-vitals flat config

Set up ESLint using eslint-config-next v16 native flat config with
no-console (warn), no-unused-vars (warn), and react/no-unescaped-entities (off).

Author: TamimEhsan

eslint.config.mjs

@@ -0,0 +1,14 @@
+import nextCoreWebVitals from "eslint-config-next/core-web-vitals";
+
+const eslintConfig = [
+  ...nextCoreWebVitals,
+  {
+    rules: {
+      "no-console": "warn",
+      "no-unused-vars": ["warn", { argsIgnorePattern: "^_" }],
+      "react/no-unescaped-entities": "off",
+    },
+  },
+];
+
+export default eslintConfig;