chore: finish frontend ESLint migration #18

Enable every plugin recommended preset and replace Biome with ESLint formatting.

Preserve API contracts and JSX whitespace; verify source, tests, builds and tooling.

src/main.tsx

@@ -5,10 +5,11 @@ import "@mantine/charts/styles.css";
 import "@mantine/dates/styles.css";
 import "@wealthledger/ui/styles.css";
 import "dayjs/locale/ru";
+
 import "./shared/i18n";
 import { App } from "./app";
 
-const root = document.getElementById("root");
+const root = document.querySelector("#root");
 
 if (!root) {
 	throw new Error("Root element not found");